Influence of lung volume on the interaction between cardiac output and cerebrovascular regulation during extreme apnoea.

NEW FINDINGS: What is the central question of this study? Does the reduction in cardiac output observed during extreme voluntary apnoea, secondary to high lung volume, result in a reduction in cerebral blood flow, perfusion pressure and oxygen delivery in a group of elite free divers? What is the main finding and its importance? High lung volumes reduce cardiac output and ventricular filling during extreme apnoea, but changes in cerebral blood flow are observed only transiently during the early stages of apnoea. This reveals that whilst cardiac output is important in regulating cerebral haemodynamics, the role of mean arterial pressure in restoring cerebral perfusion pressure is of greater significance to the regulation of cerebral blood flow. We investigated the role of lung volume-induced changes in cardiac output (Q̇) on cerebrovascular regulation during prolonged apnoea. Fifteen elite apnoea divers (one female; 185 ± 7 cm, 82 ± 12 kg, 29 ± 7 years old) attended the laboratory on two separate occasions and completed maximal breath-holds at total lung capacity (TLC) and functional residual capacity (FRC) to elicit disparate cardiovascular responses. Mean arterial pressure (MAP), internal jugular venous pressure and arterial blood gases were measured via cannulation. Global cerebral blood flow was quantified by ultrasound and cardiac output was quantified by via photoplethysmography. At FRC, stroke volume and Q̇ did not change from baseline (P > 0.05). In contrast, during the TLC trial stroke volume and Q̇ were decreased until 80 and 40% of apnoea, respectively (P < 0.05). During the TLC trial, global cerebral blood flow was significantly lower at 20%, but subsequently increased so that cerebral oxygen delivery was comparable to that during the FRC trial. Internal jugular venous pressure was significantly higher throughout the TLC trial in comparison to FRC. The MAP increased progressively in both trials but to a greater extent at TLC, resulting in a comparable cerebral perfusion pressure between trials by the end of apnoea. In summary, although lung volume has a profound effect on Q̇ during prolonged breath-holding, these changes do not translate to the cerebrovasculature owing to the greater sensitivity of cerebral blood flow to arterial blood gases and MAP; regulatory mechanisms that facilitate the maintenance of cerebral oxygen delivery.

Ascorbic acid supplementation diminishes microparticle elevations and neutrophil activation following SCUBA diving.

Predicated on evidence that diving-related microparticle generation is an oxidative stress response, this study investigated the role that oxygen plays in augmenting production of annexin V-positive microparticles associated with open-water SCUBA diving and whether elevations can be abrogated by ascorbic acid. Following a cross-over study design, 14 male subjects ingested placebo and 2-3 wk later ascorbic acid (2 g) daily for 6 days prior to performing either a 47-min dive to 18 m of sea water while breathing air (∼222 kPa N2/59 kPa O2) or breathing a mixture of 60% O2/balance N2 from a tight-fitting face mask at atmospheric pressure for 47 min (∼40 kPa N2/59 kPa O2). Within 30 min after the 18-m dive in the placebo group, neutrophil activation, and platelet-neutrophil interactions occurred, and the total number of microparticles, as well as subgroups bearing CD66b, CD41, CD31, CD142 proteins or nitrotyrosine, increased approximately twofold. No significant elevations occurred among divers after ingesting ascorbic acid, nor were elevations identified in either group after breathing 60% O2. Ascorbic acid had no significant effect on post-dive intravascular bubble production quantified by transthoracic echocardiography. We conclude that high-pressure nitrogen plays a key role in neutrophil and microparticle-associated changes with diving and that responses can be abrogated by dietary ascorbic acid supplementation.

Peripheral chemoreflex inhibition with low-dose dopamine: new insight into mechanisms of extreme apnea.

The purpose of this study was to determine the impact of peripheral chemoreflex inhibition with low-dose dopamine on maximal apnea time, and the related hemodynamic and cerebrovascular responses in elite apnea divers. In a randomized order, participants performed a maximal apnea while receiving either intravenous 2 µg·kg(-1)·min(-1) dopamine or volume-matched saline (placebo). The chemoreflex and hemodynamic response to dopamine was also assessed during hypoxia [arterial O2 tension, (PaO2 ) ∼35 mmHg] and mild hypercapnia [arterial CO2 tension (PaCO2 ) ∼46 mmHg] that mimicked the latter parts of apnea. Outcome measures included apnea duration, arterial blood gases (radial), heart rate (HR, ECG), mean arterial pressure (MAP, intra-arterial), middle (MCAv) and posterior (PCAv) cerebral artery blood velocity (transcranial ultrasound), internal carotid (ICA) and vertebral (VA) artery blood flow (ultrasound), and the chemoreflex responses. Although dopamine depressed the ventilatory response by 27 ± 41% (vs. placebo; P = 0.01), the maximal apnea duration was increased by only 5 ± 8% (P = 0.02). The PaCO2 and PaO2 at apnea breakpoint were similar (P > 0.05). When compared with placebo, dopamine increased HR and decreased MAP during both apnea and chemoreflex test (P all <0.05). At rest, dopamine compared with placebo dilated the ICA (3.0 ± 4.1%, P = 0.05) and VA (6.6 ± 5.0%, P < 0.01). During apnea and chemoreflex test, conductance of the cerebral vessels (ICA, VA, MCAv, PCAv) was increased with dopamine; however, flow (ICA and VA) was similar. At least in elite apnea divers, the small increase in apnea time and similar PaO2 at breakpoint (∼31 mmHg) suggest the apnea breakpoint is more related to PaO2 , rather than peripheral chemoreflex drive to breathe.

Intrapulmonary shunt and SCUBA diving: another risk factor?

Laboratory and field investigations have demonstrated that intrapulmonary arteriovenous anastomoses (IPAVA) may provide an additional means for venous gas emboli (VGE) to cross over to the arterial circulation due to their larger diameter compared to pulmonary microcirculation. Once thought to be the primary cause of decompression sickness (DCS), it has been demonstrated that, even in large quantities, their presence does not always result in injury. Normally, VGE are trapped in the site of gas exchange in the lungs and eliminated via diffusion. When VGE crossover takes place in arterial circulation, they have the potential to cause more harm as they are redistributed to the brain, spinal column, and other sensitive tissues. The patent foramen ovale (PFO) was once thought to be the only risk factor for an increase in arterialization; however, IPAVAs represent another pathway for this crossover to occur. The opening of IPAVAs is associated with exercise and hypoxic gas mixtures, both of which divers may encounter. The goal of this review is to describe how IPAVAs may impact diving physiology, specifically during decompression, and what this means for the individual diver as well as the future of commercial and recreational diving. Future research must continue on the relationship between IPAVAs and the environmental and physiological circumstances that lead to their opening and closing, as well as how they may contribute to diving injuries such as DCS.

Field Necropsy of the Horse.

Being able to conduct an equine field necropsy in a safe and proficient manner is a helpful skill for the equine practitioner. Use of a systematic process enables the practitioner to develop a familiarity with normal anatomic positioning and tissue appearance such that abnormalities are quickly identified. This article outlines a systematic necropsy protocol that can be used to investigate mortality events and clinical questions.

High intensity cycling before SCUBA diving reduces post-decompression microparticle production and neutrophil activation.

BACKGROUND: Venous gas emboli (VGE) have traditionally served as a marker for decompression stress after SCUBA diving and a reduction in bubble loads is a target for precondition procedures. However, VGE can be observed in large quantities with no negative clinical consequences. The effect of exercise before diving on VGE has been evaluated with mixed results. Microparticle (MP) counts and sub-type expression serve as indicators of vascular inflammation and DCS in mice. The goal of the present study is to evaluate the effect of anaerobic cycling (AC) on VGE and MP following SCUBA diving. METHODS: Ten male divers performed two dives to 18 m for 41 min, one dive (AC) was preceded by a repeated-Wingate cycling protocol; a control dive (CON) was completed without exercise. VGE were analyzed at 15, 40, 80, and 120 min post-diving. Blood for MP analysis was collected before exercise (AC only), before diving, 15 and 120 min after surfacing. RESULTS: VGE were significantly lower 15 min post-diving in the AC group, with no difference in the remaining measurements. MPs were elevated by exercise and diving, however, post-diving elevations were attenuated in the AC dive. Some markers of neutrophil elevation (CD18, CD41) were increased in the CON compared to the AC dive. CONCLUSIONS: The repeated-Wingate protocol resulted in an attenuation of MP counts and sub-types that have been related to vascular injury and DCS-like symptoms in mice. Further studies are needed to determine if MPs represent a risk factor or marker for DCS in humans.

"Quadripolar" Transcranial Electrical Stimulation for Motor Evoked Potentials.

PURPOSE: To determine if transcranial electrical stimulation (TES)-induced motor evoked potentials (MEPs) are of higher amplitude when using two electrodes as anodes and two as cathodes, known as "quadripolar stimulation." METHODS: Patients who underwent TES MEP monitoring in which control, bipolar stimulation and four variations of quadripolar stimulation were used were evaluated. The bipolar stimulation montage was C3-C4 (C3 was used as anode for stimulation first, then the polarity was switched to stimulate the contralateral side). Four quadripolar montages were used: C3/C1-C4/C2 (step 1), M3/M1-M4/M2 (step 2), C3/M1-C4/M2 (step 3), and M3/C1-M4/C2 (step 4). The area under the curve for the right foot TES MEP was compared for the various montages using descriptive statistics and Fisher exact test for proportions. RESULTS: Sixteen patients were retrospectively evaluated. The mean age as 51.6 years, range 4 to 80 years; 11 were female. The transcranial electrical stimulation MEP area under the curve for the right foot MEP was highest in the bipolar montage in 1 of 16 patients (6.3%). Meanwhile, it was highest in step 4 (M3/C1-M4/C2) in 9 of 16 patients (56.3%; P = 0.027). The highest right foot MEP area under the curve with one of the quadripolar montages was seen in 15 of 16 patients (93.8%; P = 0.0001). CONCLUSIONS: Quadripolar stimulation resulted in higher area under the curve for right foot MEP compared with conventional bipolar stimulation.

Pregnancy and Childbirth in Women With Idiopathic Intracranial Hypertension.

Background Idiopathic intracranial hypertension affects many women of childbearing age. However, the literature is sparse regarding pregnancy outcomes for these women. The goal of this study is to investigate the relationship between pregnancy outcomes in patients with a diagnosis of idiopathic intracranial hypertension. Methodology The TriNetX Research Network database was used to query 57 healthcare organizations for patients with idiopathic intracranial hypertension while pregnant (cohort 1) versus those who were pregnant without idiopathic intracranial hypertension (cohort 2). Cohorts were propensity-score matched for confounders related to pregnancy outcomes. The primary outcomes of interest were ectopic or molar pregnancy, cesarean section, abortion, preterm labor, depression, pre-eclampsia or eclampsia, and mortality. Chi-square analysis and logistic analysis were used on categorical variables. Results Ectopic/molar pregnancy was seen in 106 (1.75%) versus 117 (1.93%) (odds ratio (OR) 0.904, 95% confidence interval (CI) (0.694, 1.179), p = 0.4572) patients in cohorts 1 and 2, respectively. Cesarean section was seen in 785 (12.94%) versus 886 (14.59%) (OR 0.869, 95% CI (0.784, 0.964), p = 0.0078) patients, abortion in 536 (8.83%) versus 682 (11.24%) (OR 0.765, 95% CI (0.679, 0.862), p < 0.0001), preterm labor in 498 (8.206%) versus 668 (11.01%) (OR 0.723, 95% CI (0.640, 0.816), p < 0.0001), depression in 1,057 (17.42%) versus 1,061 (17.48%) (OR 0.995, 95% CI (0.906, 1.093), p = 0.9238), and pre-eclampsia/eclampsia in 501 (8.26%) versus 492 (8.11%) (OR 0.1.02, 95% CI (0.896, 1.161), p = 0.7657). Mortality was seen in 68 patients in cohort 1 versus 13 patients in cohort 2 (OR 5.279, 95% CI (2.913, 9.564), p < 0.0001). Conclusions This retrospective study examined pregnancy outcomes for pregnant women with a diagnosis of idiopathic intracranial hypertension. Women with idiopathic intracranial hypertension do not have an increase in rates of abortion, ectopic/molar pregnancy, cesarean section, preterm labor, or depression when compared to women without idiopathic intracranial hypertension. The mortality rate was higher in the idiopathic intracranial hypertension cohort, but still very low. This study demonstrates that pregnancy is generally well tolerated in the idiopathic intracranial hypertension population.

#Neurosurgery: A Temporal and Content Analysis of Academic Neurosurgery on Twitter.

BACKGROUND: Social media has become ubiquitous in modern medicine. Academic neurosurgery has increased adoption to promote individual and departmental accomplishments, engage with patients, and foster collaboration. We sought to quantitatively evaluate the adoption of one of the most used social media platforms, Twitter, within academic neurosurgery. METHODS: A quantitative and qualitative analysis of Twitter use across 118 academic neurosurgery departments with residency programs in the United States was performed in March 2019 and March 2021. We collated Twitter handles, Doximity residency ranking (a peer-determined ranking system), geographic location, and Twitter demographics (tweets, followers, likes, and tweet content) from before and after the coronavirus disease 2019 (COVID-19) pandemic. Tweet content was characterized by reviewers over a predetermined 6-month period. Linear regression and parametric/nonparametric tests were used for analysis. RESULTS: Departmental accounts grew 3.7 accounts per year between 2009 and 2019 (R2 = 0.96), but 43 accounts (130%) were added between 2019 (n = 33) and 2021 (n = 76). This growth, coinciding with the COVID-19 pandemic, changed the model from linear to exponential growth (R2 = 0.97). The highest-ranking programs based on Doximity were significantly more likely to have an account (P < 0.001) and have more followers (P < 0.0001). Tweet content analysis revealed prioritization of faculty/resident activity (mean 49.9%) throughout the quartiles. CONCLUSIONS: We demonstrate rapid uptake in Twitter use among U.S. academic neurosurgical departments, accelerated by COVID-19. With the impact of COVID-19, it is clear that there will be continued rapid adoption of this platform within neurosurgery, and future studies should explore the outcomes of peer collaboration, patient engagement, and dissemination of medical information.

Performing the field necropsy examination.

This article is designed to aid the practitioner by maximizing the effectiveness of field postmortem diagnostic investigations. Contents include an outline of the procedure for field necropsy of ruminants, recommended tools and supplies, and guidelines for sample collection and submission.

ß1-Blockade increases maximal apnea duration in elite breath-hold divers.

We hypothesized that the cardioselective ß1-adrenoreceptor antagonist esmolol would improve maximal apnea duration in elite breath-hold divers. In elite national-level divers (n = 9), maximal apneas were performed in a randomized and counterbalanced order while receiving either iv esmolol (150 µg·kg-1·min-1) or volume-matched saline (placebo). During apnea, heart rate (ECG), beat-by-beat blood pressure, stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were measured (finger photoplethysmography). Myocardial oxygen consumption (MV̇o2) was estimated from rate pressure product. Cerebral blood flow through the internal carotid (ICA) and vertebral arteries (VA) was assessed using Duplex ultrasound. Apnea duration improved in the esmolol trial when compared with placebo (356 ± 57 vs. 323 ± 61 s, P < 0.01) despite similar end-apnea peripheral oxyhemoglobin saturation (71.8 ± 10.3 vs. 74.9 ± 9.5%, P = 0.10). The HR response to apnea was reduced by esmolol at 10-30% of apnea duration, whereas MAP was unaffected. Esmolol reduced SV (main effect, P < 0.05) and CO (main effect; P < 0.05) and increased TPR (main effect, P < 0.05) throughout apnea. Esmolol also reduced MV̇o2 throughout apnea (main effect, P < 0.05). Cerebral blood flow through the ICA and VA was unchanged by esmolol at baseline and the last 30 s of apnea; however, global cerebral blood flow was reduced in the esmolol trial at end-apnea (P < 0.05). Our findings demonstrate that, in elite breath-hold divers, apnea breakpoint is improved by ß1-blockade, likely owing to an improved total body oxygen sparring through increased centralization of blood volume (↑TPR) and reduced MV̇o2NEW & NOTEWORTHY The governing bodies for international apnea competition, the Association Internationale pour le Développment de l'Apnée and La Confédération Mondaile des Activités Subaquatiques, have banned the use of ß-blockers based on anecdotal reports that they improve apnea duration. Using a randomized placebo-controlled trial, we are the first to empirically confirm that ß-blockade improves apnea duration. This improvement in apnea duration coincided with a reduced myocardial oxygen consumption.

Exercise before and after SCUBA diving and the role of cellular microparticles in decompression stress.

Risk in SCUBA diving is often associated with the presence of gas bubbles in the venous circulation formed during decompression. Although it has been demonstrated time-after-time that, while venous gas emboli (VGE) often accompany decompression sickness (DCS), they are also frequently observed in high quantities in asymptomatic divers following even mild recreational dive profiles. Despite this VGE are commonly utilized as a quantifiable marker of the potential for an individual to develop DCS. Certain interventions such as exercise, antioxidant supplements, vibration, and hydration appear to impact VGE production and the decompression process. However promising these procedures may seem, the data are not yet conclusive enough to warrant changes in decompression procedure, possibly suggesting a component of individual response. We hypothesize that the impact of exercise varies widely in individuals and once tested, recommendations can be made that will reduce individual decompression stress and possibly the incidence of DCS. The understanding of physiological adaptations to diving stress can be applied in different diseases that include endothelial dysfunction and microparticle (MP) production. Exercise before diving is viewed by some as a protective form of preconditioning because some studies have shown that it reduces VGE quantity. We propose that MP production and clearance might be a part of this mechanism. Exercise after diving appears to impact the risk of adverse events as well. Research suggests that the arterialization of VGE presents a greater risk for DCS than when emboli are eliminated by the pulmonary circuit before they have a chance to crossover. Laboratory studies have demonstrated that exercise increases the incidence of crossover likely through extra-cardiac mechanisms such as intrapulmonary arterial-venous anastomoses (IPAVAs). This effect of exercise has been repeated in the field with divers demonstrating a direct relationship between exercise and increased incidence of arterialization.

The impact of predive exercise on repetitive SCUBA diving.

AIM: SCUBA diving frequently involves repetitive exposures. The goal of this study was to see how exercise impacts microparticles (MPs), endothelial function and venous gas emboli (VGE) throughout multiple dives. METHODS: Sixteen divers in two groups (G1 and G2) each completed six dives, three preceded by exercise (EX) and three as controls (CON). Blood for MP analysis was collected before and after each dive. VGE were monitored via transthoracic echocardiography 30, 60 and 90 min after surfacing. Exercise before diving consisted of 60-min running including eight, 3-min intervals at 90% VO2max. RESULTS: Exercise did not have a significant impact on VGE. There was no significant difference in MP counts between EX and CON. Both groups experienced a significant decrease in MP counts in the last three dives compared to the first three (G1 P = 0·0008, G2 P = 0001). Other indices of neutrophil/platelet interaction (dual-positive CD63/41 and CD62/41) show a significant increase (P = 0·004 and 0·0001) in G2. CONCLUSION: Both groups experienced a significant decrease in MPs at all measurements in the second series of dives compared to the first, regardless of the placement of exercise. Whether this is related to an effect of suppression of MPs or exercise timing is not clear.

Role of cerebral blood flow in extreme breath holding.

The role of cerebral blood flow (CBF) on a maximal breath-hold (BH) in ultra-elite divers was examined. Divers (n = 7) performed one control BH, and one BH following oral administration of the non-selective cyclooxygenase inhibitor indomethacin (1.2 mg/kg). Arterial blood gases and CBF were measured prior to (baseline), and at BH termination. Compared to control, indomethacin reduced baseline CBF and cerebral delivery of oxygen (CDO2) by about 26% (p < 0.01). Indomethacin reduced maximal BH time from 339 ± 51 to 319 ± 57 seconds (p = 0.04). In both conditions, the CDO2 remained unchanged from baseline to the termination of apnea. At BH termination, arterial oxygen tension was higher following oral administration of indomethacin compared to control (4.05 ± 0.45 vs. 3.44 ± 0.32 kPa). The absolute increase in CBF from baseline to the termination of apnea was lower with indomethacin (p = 0.01). These findings indicate that the impact of CBF on maximal BH time is likely attributable to its influence on cerebral H+ washout, and therefore central chemoreceptive drive to breathe, rather than to CDO2.

Very Few Exercise-Induced Arterialized Gas Bubbles Reach the Cerebral Vasculature.

INTRODUCTION: Arterialization of venous gas emboli (VGE) formed after surfacing from SCUBA diving can become arterial gas emboli (AGE) through intrapulmonary arterial-venous anastomoses that open with exercise. METHODS: We recruited twenty patent foramen ovale-negative SCUBA divers and conducted a field and a laboratory study with the aim of investigating the appearance of AGE in intracranial vessels. At the field, they performed a single dive to a depth of 18-m sea water with a 47-min bottom time and a direct ascent to the surface. Transthoracic echocardiography was used to score VGE and AGE, and transcranial Doppler was used to visualize middle and posterior cerebral arteries with automated objective bubble detection. Observations were conducted for 45-min after dive at rest and at the laboratory after agitated saline injection at rest and throughout an incremental cycle supine exercise test until exhaustion and for 10 min of recovery. RESULTS: After resurfacing, all divers presented endogenous VGE and arterialization was present in three divers. Saline contrast injection led to AGE in nine of 19 subjects at rest. AGE that reached the cerebral arteries after dive were recorded in two divers at 60 W, three at 90 W, five at 120 W, six at 150 W, and four at 180 W and in three, four, five, nine, and nine, respectively, after saline contrast injection in the laboratory. All divers had AGE grades of 1 or 2, and only single AGE reached the cerebral vasculature. CONCLUSIONS: These data suggest that few emboli of venous origin reach the brain through exercise-induced intrapulmonary arterial-venous anastomoses but cerebral embolization is not high risk in the studied population.

The impact of consecutive freshwater trimix dives at altitude on human cardiovascular function.

Self-contained underwater breathing apparatus (SCUBA) diving is regularly associated with numerous asymptomatic changes in cardiovascular function. Freshwater SCUBA diving presents unique challenges compared with open sea diving related to differences in water density and the potential for dive locations at altitude. The aim of this study was to evaluate the impact of freshwater trimix diving at altitude on human cardiovascular function. Ten divers performed two dives in consecutive days at 294 m altitude with the surface interval of 24 h. Both dives were at a depth of 45 m with total dive time 29 and 26 min for the first and second dive, respectively. Assessment of venous gas embolization, hydration status, cardiac function and arterial stiffness was performed. Production of venous gas emboli was low, and there were no significant differences between the dives. After the first dive, diastolic blood pressure was significantly reduced, which persisted up to 24 h. Left ventricular stroke volume decreased, and heart rate increased after both dives. Pulse wave velocity was unchanged following the dives. However, the central and peripheral augmentation index became more negative after both dives, indicating reduced wave reflection. Ejection duration and round trip travel time were prolonged 24 h after the first dive, suggesting longer-lasting suppression of cardiac and endothelial function. This study shows that freshwater trimix dives with conservative profiles and low venous gas bubble loads can result in multiple asymptomatic acute cardiovascular changes some of which were present up to 24 h after dive.

Regulation of brain blood flow and oxygen delivery in elite breath-hold divers.

The roles of involuntary breathing movements (IBMs) and cerebral oxygen delivery in the tolerance to extreme hypoxemia displayed by elite breath-hold divers are unknown. Cerebral blood flow (CBF), arterial blood gases (ABGs), and cardiorespiratory metrics were measured during maximum dry apneas in elite breath-hold divers (n=17). To isolate the effects of apnea and IBM from the concurrent changes on ABG, end-tidal forcing ('clamp') was then used to replicate an identical temporal pattern of decreasing arterial PO2 (PaO2) and increasing arterial PCO2 (PaCO2) while breathing. End-apnea PaO2 ranged from 23 to 37 mm Hg (30 ± 7 mm Hg). Elevation in mean arterial pressure was greater during apnea than during clamp reaching +54 ± 24% versus 34 ± 26%, respectively; however, CBF increased similarly between apnea and clamp (93.6 ± 28% and 83.4 ± 38%, respectively). This latter observation indicates that during the overall apnea period IBM per se do not augment CBF and that the brain remains sufficiently protected against hypertension. Termination of apnea was not determined by reduced cerebral oxygen delivery; despite 40% to 50% reductions in arterial oxygen content, oxygen delivery was maintained by commensurately increased CBF.

Effect of Maximal Apnoea Easy-Going and Struggle Phases on Subarachnoid Width and Pial Artery Pulsation in Elite Breath-Hold Divers.

PURPOSE: The aim of the study was to assess changes in subarachnoid space width (sas-TQ), the marker of intracranial pressure (ICP), pial artery pulsation (cc-TQ) and cardiac contribution to blood pressure (BP), cerebral blood flow velocity (CBFV) and cc-TQ oscillations throughout the maximal breath hold in elite apnoea divers. Non-invasive assessment of sas-TQ and cc-TQ became possible due to recently developed method based on infrared radiation, called near-infrared transillumination/backscattering sounding (NIR-T/BSS). METHODS: The experimental group consisted of seven breath-hold divers (six men). During testing, each participant performed a single maximal end-inspiratory breath hold. Apnoea consisted of the easy-going and struggle phases (characterised by involuntary breathing movements (IBMs)). Heart rate (HR) was determined using a standard ECG. BP was assessed using the photoplethysmography method. SaO2 was monitored continuously with pulse oximetry. A pneumatic chest belt was used to register thoracic and abdominal movements. Cerebral blood flow velocity (CBFV) was estimated by a 2-MHz transcranial Doppler ultrasonic probe. sas-TQ and cc-TQ were measured using NIR-T/BSS. Wavelet transform analysis was performed to assess cardiac contribution to BP, CBFV and cc-TQ oscillations. RESULTS: Mean BP and CBFV increased compared to baseline at the end of the easy phase and were further augmented by IBMs. cc-TQ increased compared to baseline at the end of the easy phase and remained stable during the IBMs. HR did not change significantly throughout the apnoea, although a trend toward a decrease during the easy phase and recovery during the IBMs was visible. Amplitudes of BP, CBFV and cc-TQ were augmented. sas-TQ and SaO2 decreased at the easy phase of apnoea and further decreased during the IBMs. CONCLUSIONS: Apnoea increases intracranial pressure and pial artery pulsation. Pial artery pulsation seems to be stabilised by the IBMs. Cardiac contribution to BP, CBFV and cc-TQ oscillations does not change throughout the apnoea.

Association of microparticles and neutrophil activation with decompression sickness.

Decompression sickness (DCS) is a systemic disorder, assumed due to gas bubbles, but additional factors are likely to play a role. Circulating microparticles (MPs)--vesicular structures with diameters of 0.1-1.0 µm--have been implicated, but data in human divers have been lacking. We hypothesized that the number of blood-borne, Annexin V-positive MPs and neutrophil activation, assessed as surface MPO staining, would differ between self-contained underwater breathing-apparatus divers suffering from DCS vs. asymptomatic divers. Blood was analyzed from 280 divers who had been exposed to maximum depths from 7 to 105 meters; 185 were control/asymptomatic divers, and 90 were diagnosed with DCS. Elevations of MPs and neutrophil activation occurred in all divers but normalized within 24 h in those who were asymptomatic. MPs, bearing the following proteins: CD66b, CD41, CD31, CD142, CD235, and von Willebrand factor, were between 2.4- and 11.7-fold higher in blood from divers with DCS vs. asymptomatic divers, matched for time of sample acquisition, maximum diving depth, and breathing gas. Multiple logistic regression analysis documented significant associations (P < 0.001) between DCS and MPs and for neutrophil MPO staining. Effect estimates were not altered by gender, body mass index, use of nonsteroidal anti-inflammatory agents, or emergency oxygen treatment and were modestly influenced by divers' age, choice of breathing gas during diving, maximum diving depth, and whether repetitive diving had been performed. There were no significant associations between DCS and number of MPs without surface proteins listed above. We conclude that MP production and neutrophil activation exhibit strong associations with DCS.

The effects of nitroglycerin, norepinephrine and aminophylline on intrapulmonary arteriovenous anastomoses in healthy humans at rest.

We have investigated the effects of the intravenous infusion of nitroglycerin (NTG), norepinephrine (NE) and aminophylline (AMP) on the opening and recruitment of intrapulmonary arteriovenous anastomoses (IPAVA) in healthy humans at rest. In ten volunteers saline contrast echocardiography was performed during administration of two doses of the NTG (3µgkg(-1)min(-1) and 6µgkg(-1)min(-1)) and NE (0.1µgkg(-1)min(-1) and 0.25µgkg(-1)min(-1)) as well as 30min following the administration of AMP at rate of 6mgkg(-1). Echocardiography was used to assign bubble scores (0-5) based on the number and spatial distribution of bubbles in the left ventricle. Doppler ultrasound was used to estimate pulmonary artery systolic pressure. Using a Finometer the following hemodynamic parameters were assessed: heart rate, stroke volume, cardiac output, total peripheral resistance as well as systolic, diastolic and mean arterial pressure. The most important finding from the current study was that nitroglycerin, norepinephrine and aminophylline in the applied doses were not found to promote IPAVA opening in healthy humans at rest.