Mechanical and physiological effect of partial pressure suit: Experiment and numerical study.

BACKGROUND: During high-altitude flight, the protection of the pilot is vital. A partial pressure suit may affect human physiology, especially circulatory physiology. OBJECTIVE: The purpose of this study was to investigate how a partial pressure suit works. METHOD: Ten subjects took part in the flight simulation experiments. Counter pressure at the chest, abdomen, thigh and shank were detected, together with physiological parameters such as heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR). A numerical model was also established to simulate hemo-physiological effects of the partial pressure suit. RESULTS: The experiment's results show the non-uniform counter pressure distribution in different parts of the body. There is a linear, proportional relation between TPR and the pressurizing level. HR and MAP increase along with that of the pressure level. SV and CO decrease with the increase of the pressure level. The numerical model simulated the physiological effect of a partial pressure suit. The results were verified by experiment data. The simulation estimated the change of blood flow with the pressure level. CONCLUSIONS: The numerical model provides a potential way to improve the protection of pilots.

A cluster randomized controlled trial of the non-pneumatic anti-shock garment for obstetric haemorrhage: sub-analysis of the Zimbabwean Arm.

Objectives: To determine whether earlier application of the Non-pneumatic Anti-Shock Garment (NASG) at clinic level compared to the referral hospital level reduces maternal morbidity and mortality and recovery time from shock due to severe Obstetric Haemorrhage (OH) and to determine the safety of the NASG when applied at clinic level. Design: A cluster Randomized Controlled Trial (RCT) Setting: Harare and Parirenyatwa Referral Hospitals (RH) in Harare and the twelve Harare City Council clinics that offer maternity care. Subjects: Women who had suffered severe OH at clinic level and were being transferred to a Referral Hospital (RH). Iterventions: The clinics were randomized into two groups. In the early NASG group eligible women were given the standard management for OH and had the NASG applied at the clinic level before transport to RH. In the control group, eligible women were given the standard management for OH at the clinic level, transferred to the RH, and received the NASG at the RH. All women received equivalent OH/hypovolemic shock management at the RH. Main Outcome Measures: The main outcome measures were maternal mortality and morbidity, blood loss, recovery from shock and the occurrence of side effects whilst in the NASG. Results: There were few maternal deaths and morbidities, and no statistically significant differences between the two groups were noted. Women in the early NASG group spent a statistically significant shorter time in the NASG at referral hospital level (OR 0.64, 95% CI 0.52 - 0.79, p < 0.001) and had a non-significant 40% faster recovery from shock (HR 1.39; 95% CI 0.98-1.97, p=0.07). There were no differences in reported side effects. Conclusion: Earlier NASG application at the clinic level was associated with faster recovery from shock in women who had suffered severe OH and appears safe to use.

Pressure garments for use in the treatment of hypertrophic scars--a review of the problems associated with their use.

Pressure garments have been the mainstay of hypertrophic scar treatment since the 1970s. However, there are many problems associated with their use. This is the first in a series of papers on pressure garments that will review the literature published to date on the origins of pressure garments for hypertrophic scar treatment and the problems associated with current pressure garment use.

Cardiovascular effects of anti-G suit inflation at 1 and 2 G.

We sought to determine to which pressure a full-coverage anti-G suit needs to be inflated in order to obtain the same stroke volume during a brief exposure to twice the normal gravity (2 G) as that at 1 G without anti-G suit inflation. Nine sitting subjects were studied at normal (1 G) and during 20 s of exposure to 2 G. They wore anti-G suits, which were inflated at both G-levels to the following target pressures: 0, 70, 140 and 210 mmHg. Stroke volume was computed from cardiac output, which was measured by rebreathing. Heart rate and mean arterial pressure at heart level were recorded. Inflation to 70 mmHg compensated for the decrease in stroke volume and cardiac output caused by hypergravity. Mean arterial pressure at heart level was comparable at 1 G and at 2 G and increased gradually and similarly with inflation (P<0.001) at both gravity levels. Thus, anti-G suits act by increasing both preload and afterload but the two effects counteract each other in terms of cardiac output, so that cardiac output at 2 G is maintained at its 1 G level. This effect is reached already at 70 mmHg of inflation. Greater inflation pressure further increases mean arterial pressure at heart level and compensates for the increased difference in hydrostatic pressure between heart and head in moderate hypergravity.

Inter- and intraregional ventilation inhomogeneity in hypergravity and after pressurization of an anti-G suit.

This study assessed the effects of increased gravity in the head-to-foot direction (+G(z)) and anti-G suit (AGS) pressurization on functional residual capacity (FRC), the volume of trapped gas (V(TG)), and ventilation distribution by using inert- gas washout. Normalized phase III slope (Sn(III)) analysis was used to determine the effects on inter- and intraregional ventilation inhomogeneity. Twelve men performed multiple-breath washouts of SF(6) and He in a human centrifuge at +1 to +3 G(z) wearing an AGS pressurized to 0, 6, or 12 kPa. Hypergravity produced moderately increased FRC, V(TG), and overall and inter- and intraregional inhomogeneities. In normogravity, AGS pressurization resulted in reduced FRC and increased V(TG), overall, and inter- and intraregional inhomogeneities. Inflation of the AGS to 12 kPa at +3 G(z) reduced FRC markedly and caused marked gas trapping and intraregional inhomogeneity, whereas interregional inhomogeneity decreased. In conclusion, increased +G(z) impairs ventilation distribution not only between widely separated lung regions, but also within small lung units. Pressurizing an AGS in hypergravity causes extensive gas trapping accompanied by reduced interregional inhomogeneity and, apparently, results in greater intraregional inhomogeneity.

Heat stress effects for USAF anti-G suits with and without a counter-pressure vest.

BACKGROUND: Aircrew have reported increased heat stress when wearing the USAF Combined Advanced Technology Enhanced Design G-Ensemble or COMBAT EDGE (CE). The perceived thermal burden has been attributed to the fact that CE includes an inflatable counter-pressure vest to ease the work of positive pressure breathing during G (PBG). This study compared the heat load of CE with that of the standard USAF anti-G system (STD) without the vest, and measured heat stress effects on G-tolerance in both suits. METHODS: This study had 12 subjects (6 of them aircrew) who participated. Simulated preflight thermal stress (20 min walking at 35 degrees C with 85% relative humidity and radiant heat) was followed by return to a cooler environment (21 degrees C). G-tolerance and subjective stress levels were determined on the human centrifuge before and after the heat stress. Body weight, rectal and skin temperatures, and blood parameters were also assessed. RESULTS: Baseline relaxed tolerance for +Gz gradual onset runs (GORs) were (mean +/- SD) 7.6 +/- 1.3 G for CE and 7.1 +/- 0.8 G for STD (p < 0.05). Maximal rectal temperature following heat stress peaked at 38.1 +/- 0.4 degrees C for both CE and STD, and mean nude weight loss was 1.10 +/- 0.24 kg for both. Relaxed GOR tolerances after heat stress were 7.1 +/- 1.3 for CE and 6.3 +/- 0.9 for STD (p < 0.01). The heat stress significantly reduced G tolerance for both CE and STD (p < 0.01). CONCLUSIONS: Simulated preflight activity in hot conditions revealed no significant difference between CE and STD with regard to maximal core and skin temperature elevations or dehydration levels. CE supported a significantly higher baseline relaxed G-tolerance than STD, an advantage that persisted after heat stress and dehydration.

Premature ventricular contractions during +Gz with and without pressure breathing and extended coverage anti-G suit.

BACKGROUND: High +Gz is known to provoke cardiac dysrhythmias. Pressure breathing during G (PBG) and extended coverage anti-G suits (ECGS) are used to enhance +Gz-endurance and reduce fatigue during high +Gz flying. It is not known whether PBG in combination with ECGS increases the risk for premature ventricular contractions (PVC). HYPOTHESIS: PBG in combination with ECGS increases the risk of PVCs during high +Gz-loads. METHODS: Retrospective data were obtained from 14 subjects exposed to three different simulated aerial combat sorties each, in the centrifuge with a standard anti-G suit ensemble or with PBG in combination with ECGS. Each sortie consisted of a gradual onset G-exposure (GOR) and three simulated aerial combat maneuvers (SACM) containing four cycles of a +4.5 to +7 GzSACM; four cycles of +4 to +9 Gz tactical aerial combat maneuver (TACM) with several rapid transitions from +4 or +5 Gz to +8 or +9 Gz; and four cycles of +5 to +9 Gz SACM (5-9 SACM) with four cycles. ECG was recorded during the +Gz exposures to reveal any cardiac dysrhythmias. RESULTS AND CONCLUSIONS: No PVCs occurred during the GORs. During 4.5-7 SACMs, TACMs, and 5-9 SACMs there were 83, 50, and 24 PVCs with standard equipment, respectively, and 63, 54, and 39 PVCs with PBG and ECGS, respectively. There was no statistically significant difference between the equipment in any of the different types of +Gz exposures. No episodes of supraventricular tachycardia or relative bradycardia were found with either equipment.

Male/female SACM endurance comparison: support for the Armstrong Laboratory modifications to the CSU-13B/P anti-G suit.

BACKGROUND: The standard anti-G suit (CSU-13B/P) was designed based on male body structure. Females differ from males with respect to body proportionality. In Armstrong Laboratory (AL) studies, females have terminated centrifuge simulated air combat maneuvers (SACM) because of anti-G suit (CSU-13B/P modified according to original T.O. 14P3-6-121)(OTO) discomfort. AL modifications to the suit have since been adopted in the OTO in an attempt to provide females a best-fit suit (AL Mod). The study examined male/female SACM endurance with females wearing both the OTO and the AL Mod suits. METHODS: There were 6 females and 8 males who performed a +5.0 to +9.0 Gz SACM to fatigue using the anti-G straining maneuver with anti-G suit inflation. The females performed in both the OTO and AL Mod suits while the males performed in the OTO suit only (OTO was their best-fit suit). RESULTS: Wearing the OTO, males performed the SACM significantly longer than the females, three of whom reported severe suit discomfort. However, when the females wore the AL Mod suit, their SACM endurance almost doubled over their OTO performance and none reported suit discomfort. When wearing their best-fit suits, there was no significant gender difference in SACM endurance. CONCLUSIONS: These data support the efficacy of the AL modifications to the CSU-13B/P anti-G suit through greatly improved performance during the +5.0 to +9.0 SACM in females. These data also suggest that, in the small sample examined, when fitted with a best-fit anti-G suit, females can endure the +5.0 to +9.0 SACM to the same degree as males.

[Reduced muscular oxygen tension and nerve impulse transmission from antishock hose. Reduction of oxygen tension in the tibial muscle and impulse transmission in the peroneal nerve from pneumatic -1 pressure from antishock hose]. / Muskuläre Sauerstoffspannung und nervale Impulsfortleitung bei Einsatz der Antischockhose. Verminderung der Sauerstoffspannung im M. tibialis anterior und Einschränkung der Impulsfortleitung im N. peronaeus profundus infolge pneumatischer Druckeinwirkung durch Antischockhose.

OBJECT OF THE STUDY: The aim of the study was to assess, whether the pneumatic pressure of an antishock-trouser (AST) of 20-40 mm Hg induces a decreased oxygenation of the anterior tibial muscle and attenuates muscular response potential (MRP) of n. peronaeus profundus? METHODS: Among 22 normotensive, healthy volunteers the AST were tested by applying pressure values between 0 and 100 mm Hg and measuring the intracompartmental pressure, the muscular oxygen pressure as well as the MRP by electroneurographic means within a period of 6 hours. RESULTS: The median initial intracompartmental pressure value of the m. tibialis anterior was 12.0 mm Hg (Q25%/Q75%: 8.9/17.3), the muscular oxygen pressure 14.8 mm Hg (Q25%/Q75%: 11.5/22.0). Transmission of the pneumatic AST-leg segment pressure to the muscle: 97.7% (Q25%/Q75%: 89.2/99.8). Already in the low AST pressure field (20-40 mm Hg) a severe hypoxia occurred in one case. A reduction of MRP was noticed at an AST pressure rate of 10 mm Hg. In 5 of 6 cases AST pressure values of 60 mm Hg led to pathological pO2-values within 5-20 minutes. Almost without exception AST-pressure rates < 60 mm Hg resulted in an anoxia of the muscle and loss of the MRP. CONCLUSIONS: We should demand that the AST are only applied with models where the pressure generated within the single segments can be controlled by pressure gauge. The application of the AST seems to be justified for polytraumatised in severe haemorrhagic shock where the risk of a local tissue ischemia with systemical consequences must deliberately be accepted.

Influence of a reduced G-suit pressure schedule on G-duration tolerance using enhanced G-protection ensembles.

BACKGROUND: Reducing pressure to enhanced G-protection ensembles may diminish potential undesirable physiologic effects, as well as improve wear comfort and garment durability. HYPOTHESIS: G-duration tolerance will not be affected by reducing pressure to the Swedish tactical flight combat suit (TFCS). A second objective tested the similarity in G-duration tolerance between the TFCS and Combined Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) combined with a prototype enhanced coverage G-suit. METHODS: There were 12 Swedish pilots (mean = 30 yr) who experienced gradual onset (+0.1 G.s-1) runs (GOR) to +9 Gz, rapid (+6 G.s-1) onset runs (ROR) and simulated aerial combat maneuvers (SACM) with +5 to +9 Gz cycles. The GOR and ROR profiles had a sustained times of 60 s after reaching +9 Gz. RESULTS: GOR duration tolerance was statistically decreased (p < 0.01) by the lower pressure (1.1 psig.G-1) when compared to standard pressure (1.5 psig.G-1). No statistical difference between TFCS and COMBAT EDGE was observed during the GOR trials. For all conditions, during the RORs, 90% of the subjects completed at least 30 s at +9 Gz. Many technical or medical difficulties during SACM trials limited statistical treatment of these data. However, no obvious among-condition differences were observed. Noteworthy among SACM trials were those of 3 subjects enduring more than 9 min before stopping; one completing 12.5 min (35 cycles). Neither heart rate, blood pressure, nor perceived exertion data revealed a condition-effect difference. CONCLUSION: Moderately reduced pressure to the extended coverage anti-G suit, combined with positive pressure breathing, may yield decreased G-tolerance results during laboratory evaluation; however, observed differences are sufficiently small they are likely operationally insignificant.

[Antigravity suit used for neurosurgical operations in sitting position]. / Zastosowanie lotniczego ubioru przeciwprzeciazeniowego w operacjach neurochirurgicznych w pozycji siedzacej.

The aviator's antigravity suit (G-suit) was used for 40 operations on neurosurgical patients operated on in sitting position. The G-suit was filled with air to 0.2 atmosphere (20 kPa) pressure in 26 cases, and 0.3 atm. (30 kPa) in 14 cases. In all cases G-suit filling was followed by central venous pressure rise and mean arterial pressure rise. Venous air embolism was found in 5 (12.5%) patients. No other complications connected with the use of G-suit were observed.

Preventable death evaluation of the appropriateness of the on-site trauma care provided by Urgences-Santé physicians.

The study is based on 44 preventable deaths occurring in a cohort of 360 patients with major trauma. These cases were reviewed by a committee of nine experts. The mean Injury Severity Score (ISS) was 28, and most cases had injuries to the head/neck (68%) and chest (64%). The mean (+/- SD) observed prehospital times, and those considered the maximum allowable by the committee, were 40.6 +/- 12.0 minutes for head/neck injuries and 23.9 +/- 12.2 minutes for chest injuries (p < 0.05). Intravenous (i.v.) lines were started in 38 (86%) of the patients. The committee classified this procedure as harmful for 16 (42%) and neutral for 19 (50%). Among the 18 (46%) that were intubated, this intervention was considered harmful for 17% and neutral for 39%. In two of the three patients for whom a pneumatic antishock garment was applied, this procedure was considered harmful. Of the 34 patients that required direct transport at a level I trauma center, 50% were transferred to such a hospital. These results show significant prehospital delays and high rates of inappropriate IV line initiation and intubation in trauma patients receiving on-site care by physicians. We conclude that prehospital care protocols for trauma patients should emphasize prompt transport and specific on-site care algorithms.

Pneumatic antishock garment-associated compartment syndrome in uninjured lower extremities.

Pneumatic antishock garment-associated compartment syndrome is a rare and yet underrecognized complication that when it occurs, frequently results in myonecrosis and loss of limb function, and occasionally loss of a limb or even death. We report a case of pneumatic antishock garment-associated compartment syndrome in a trauma patient without lower extremity injury and review similar published reports. It is only with a high index of suspicion, early recognition, and prompt treatment of this complication by fasciotomy and proper wound care that associated morbidity and potential mortality of this complication can be prevented or minimized.

Fluid and electrolyte deficit with prolonged pneumatic antishock garment application.

OBJECTIVE: When trauma victims are within 1 hour of definitive surgical care, prehospital pneumatic antishock garment (PASG) application has not improved outcome. A resuscitative role for PASG has been suggested when transport time is longer (e.g., 4 hours). We assessed the fluid and electrolyte cost of treating posthemorrhagic hypotension with the PASG in 16 anesthetized Yorkshire piglets (30 to 32 kg). DESIGN: Hypotension [30 mm Hg drop in carotid arterial blood pressure (CBP)] was produced by arterial line bleeding. Hemodynamics, serum electrolytes, lactate, and tissue edema (limb circumference) were monitored. MATERIALS AND METHODS: In eight animals (group 1), PASG was inflated to maintain prebleed CBP for 4 hours. In group 2, the hypotension was untreated for 4 hours. After 4 hours, shed blood (over a period of 15 minutes) and normal saline (1.5 mL/kg/minute) were infused until CBP returned to normal baseline values. MEASUREMENTS AND MAIN RESULTS: Shed blood alone did not restore baseline CBP. Serum K+ increased from a baseline of 3.9 to 9.1 mmol/L in group 1, with no significant change in group 2. Serum lactate rose from 1.8 to 24.1 and from 1.7 to 6.8 mmol/L in groups 1 and 2, respectively. After 4 1/2 hours, an increase in thigh circumference (6.4 +/- 1.4 vs. 1.9 +/- 1.0 mm) and intravenous fluid required after returning shed blood (626 +/- 36 vs. 324 +/- 22 mL) was greater in group 1 (means +/- SD, p < 0.05). Other serum electrolyte values were similar for the two groups. CONCLUSIONS: We conclude that fluid deficit, lactic acidosis, tissue edema, and hyperkalemia are all greater with prolonged PASG application when compared with the untreated hypotensive state. These findings must be considered when suggesting more prolonged PASG application.