Reflex influence of carotid baroreceptor inactivation on respiratory resistance in humans.

Our previous study demonstrated that selective carotid baroreceptors activation decreases airway resistance. The aim of the present study was to evaluate the effect of carotid baroreceptor inactivation on the reflex change of respiratory resistance. Twenty healthy men aged between 20 and 25 were included in the study. Selective inactivation of carotid baroreceptors was induced by generating a positive pressure of 40 mmHg for 5 s in two capsules placed bilaterally on the neck over the bifurcation of the carotid arteries. The oscillatory method (Siregnost FD5, Siemens) was used to measure continuously respiratory resistance. Inactivation of carotid baroreceptors produced a short increase in respiratory resistance by 0.39 +/- 0.01(SE) mbar/l/s, i.e., 21.7% above the resting level. We conclude that in humans, carotid baroreceptors might have a background contribution to bronchodilator tone. This observation seems to be important for clinical situations of impairment of baroreflex function.

Impairment of the baroreflex control of human respiratory resistance with age.

BACKGROUND: The mechanism responsible for the central baroreflex resetting with age are an area of limited knowledge. We previously demonstrated that in subjects aged above 50 the airway resistance did not change in response to baroreceptor activation, whereas in younger volunteers the airway resistance significantly decreased. OBJECTIVE: The aim of the present study was to evaluate the effect of carotid baroreceptor inactivation on the reflex change of respiratory resistance, in the course of aging. MATERIAL AND METHODS: 80 healthy men, divided in four groups: aged 20-30 (Group I), 31-40 (Group II), 41-50 (Group III), and 51-60 (Group IV) were included in the study. The selective inactivation of carotid baroreceptors was induced by generating a positive pressure of 40 mmHg for 5 s in two capsules placed bilaterally on the neck over the bifurcation of the carotid arteries. The oscillatory method (Siregnost FD5, Siemens) was used to measure continuously respiratory resistance. RESULTS: Inactivation of carotid baroreceptors produced a short increase in respiratory resistance by 0.38 +/- 0.01SE mbar/l/s, i.e., 21.7% above the resting level in Group I and by 0.25 +/- 0.01 mbar/l/s in Group II. In the two older groups (III and IV) respiratory resistance did not change in response to baroreceptors inactivation. CONCLUSIONS: In humans aged above 40, carotid baroreceptors do not contribute to bronchodilator tone, which causes imbalance between the activities of upper airway and chest wall inspiratory muscles leading to a collapsing effect on the upper airway.

Cardiovascular regulation and body temperature: evidence from a nap vs. sleep deprivation randomized controlled trial.

In this study we set out to understand is sleep fragmentation affects the cardiovascular regulation and circadian variability of core body temperature more or less than sleep deprivation. 50 healthy men (age 29.0+/-3.1 years; BMI 24.3+/-2.1 kg/m(2)) participated in a 3-day study that included one adaptative night and one experimental night involving randomization to: sleep deprivation (SD) and sleep fragmentation (SF). The evaluation included hemodynamic parameters, measures of the spectral analysis of heart rate and blood pressure variability, and the sensitivity of arterial baroreflex function. Core body temperature (CBT) was measured with a telemetric system. SF affects heart rate (61.9+/-5.6 vs 56.2+/-7.6, p<0.01) and stroke index (52.7+/-11.1 vs. 59.8+/-12.2, p<0.05) with significant changes in the activity of the ANS (LF-sBP: 6.0+/-5.3 vs. 3.4+/-3.7, p<0.05; HF-sBP: 1.8+/-1.8 vs 1.0+/-0.7, p<0.05; LF-dBP: 5.9+/-4.7 vs. 3.5+/-3.2, p<0.05) more than SD. Post-hoc analysis revealed that after SD mean value of CBT from 21:30 to 06:30 was significantly higher compared to normal night's sleep and SF. In healthy men SF affects the hemodynamic and autonomic changes more than SD. Sympathetic overactivity is the proposed underlying mechanism.

Cardiovascular regulation and body temperature: evidence from a nap vs. sleep deprivation randomized controlled trial.

In this study we set out to understand is sleep fragmentation affects the cardiovascular regulation and circadian variability of core body temperature more or less than sleep deprivation. 50 healthy men (age 29.0+/-3.1 years; BMI 24.3+/-2.1 kg/m(2)) participated in a 3-day study that included one adaptative night and one experimental night involving randomization to: sleep deprivation (SD) and sleep fragmentation (SF). The evaluation included hemodynamic parameters, measures of the spectral analysis of heart rate and blood pressure variability, and the sensitivity of arterial baroreflex function. Core body temperature (CBT) was measured with a telemetric system. SF affects heart rate (61.9+/-5.6 vs. 56.2+/-7.6, p<0.01) and stroke index (52.7+/-11.1 vs. 59.8+/-12.2, p<0.05) with significant changes in the activity of the ANS (LF-sBP: 6.0+/-5.3 vs. 3.4+/-3.7, p<0.05; HF-sBP: 1.8+/-1.8 vs. 1.0+/-0.7, p<0.05; LF-dBP: 5.9+/-4.7 vs. 3.5+/-3.2, p<0.05) more than SD. Post hoc analysis revealed that after SD mean value of CBT from 21:30 to 06:30 was significantly higher compared to normal night's sleep and SF. In healthy men SF affects the hemodynamic and autonomic changes more than SD. Sympathetic overactivity is the proposed underlying mechanism.

Does night-shift work induce apnea events in obstructive sleep apnea patients?

The aim of the present study was to determine the direct effect of night-work on the occurrence of obstructive apneas during sleep after a night shift in fast-rotating shift workers with sleep-related breathing disorders. Eight obstructive sleep apnea patients were examined with the use of a polysomnograph during sleep under two conditions: after day-shift work and after night-shift work. Both sleep studies were conducted within 2 to 3 weeks of each other. In four of the 8 subjects, during sleep after a night-shift, an increase in apnea/hypopnea index was found. Night work significantly increased several breathing variables: total duration of obstructive apneas during REM sleep, mean duration of obstructive apneas during arousal, and apnea index during arousal. We conclude that in a subpopulation of sleep apnea patients, acute sleep deprivation may worsen obstructive sleep apnea index.

Low amplitude daily changes in reflex ventilatory response to progressive isocapnic hypoxia.

Daily changes in reflex ventilatory responses to hypoxia were studied in 56 young healthy men participated. A rebreathing technique--progressive isocapnic hypoxia--was used to measure hypoxic chemoreflex reactivity. The measurements were repeated every 3 hours during a 24-hour period. The ventilatory response to hypoxia--analyzed as the relationships (slope) MV/SaO2 (minute ventilation/arterial oxygen blood saturation) and P0.1/SaO2 (mouth occlusion pressure/oxygen arterial blood saturation) remained relatively stable throughout the examined period exhibiting low-amplitude differences from one another with the maximum variation at 12:00 hours.

Daily changes in cardiac and vascular blood pressure components during breath holding episodes in obstructive sleep apnea patients after day-shift and night-shift work.

We evaluated daily variability in the cardiovascular response to arterial chemoreceptors activation during breath holding in shift workers who were obstructive sleep apnea patients. Ten patients and 10 weight and age-matched control subjects were enrolled in the study. The experimental sessions consisted of 10 episodes of breath holding on inspiration interspersed with 1 min free breathing periods, repeated every 6 h: at 0.00, 6.00, 12.00, 18.00 hours. The subjects were examined under two experimental protocols: after day-shift work and after night-shift work (36 h of sleep deprivation). Blood pressure (System Portapres), ECG, and arterial hemoglobin oxygen saturation were monitored continuously. Data analysis were based on Smietanowski procedures written in the 4-th generation script language of MATLAB environment. The two methods introduced by Smietanowski a enabled symbolic description of cardiovascular regulatory mechanisms as cardiac, vascular, or mixed type control (BBC), and allowed quantifying relative contributions of cardiac and vascular components in the blood pressure variability. During the part of the study conducted after day-shift work, repetitive apneas led to a significantly greater increase in blood pressure in the sleep apnea patients, as compared with the controls. BBC analysis demonstrated that in the patients the domination of vascular influences during breath holding periods reached 70+/-2.0% and was significantly greater in comparison with the control group: 56+/-2.8 (P<0.01). However, contribution of cardiac component in the blood pressure response to breath holding was greater in the control group: 32+/-2% as compared with the 18+/-2% in the group of patients (P<0.01). Under the conditions of sleep deprivation (night-work shift), greater blood pressure responses to breath holding were observed in all subjects, but they were larger in the group of sleep apnea patients. The cardiovascular responses to hypoxia during breath holding showed daily variability: greater responses at 12.00 and 18.00 declined at 0.00 and 6.00 h. BBC analysis indicated a greater domination of vascular component in the blood pressure response in patients: 71+/-2.8% vs. 58+/-2% in controls. The contribution of cardiac component predominated in the control group: 27+/-3% vs. 19+/-1% in patients.

Changes in upper airway resistance during progressive normocapnic hypoxia in patients with obstructive sleep apnoea syndrome.

The responses of the upper airway to progressive normocapnic hypoxia were studied in 6 healthy men and in 6 patients with obstructive sleep apnoea syndrome (OSAS). The upper airway resistance was calculated by the ratio of the laryngeal pressure (measured using a catheter introduced into oesophagus) to the inspiratory flow. Additionally, genioglossal EMG activity (GG-EMG) was measured and analysed. The changes of all variables were analysed individually for each subject. The OSAS patients showed reduced ventilatory response, GG-reactivity and changes in upper airway resistance during progressive hypoxia. It is concluded that impaired reactivity to hypoxic activation (probably due to the process of adaptation of carotid chemoreceptors to nocturnal hypoxia), might reduce the defence abilities of OSAS patients against episodes of obturation in upper airway and obstructive apnoea events.

Impaired blood pressure variability in chronic fatigue syndrome--a potential biomarker.

INTRODUCTION: Autonomic dysfunction is common in chronic fatigue syndrome (CFS). This study set out to derive an autonomic biomarker using a comprehensive assessment of heart rate and blood pressure variability. METHODS: Heart rate and non-invasive continuous blood pressure measurements (task force monitor) at rest and on standing were performed in CFS (Fukuda n = 68) and matched controls (n = 68) to derive high frequency (HF; parasympathetic) and low frequency (LF; sympathetic) heart rate variability (HRV), systolic (SBPV) and diastolic (DBPV) blood pressure variability. Variables of significance were combined using receiver operator curves to explore the diagnostic utility of parameters particularly at rest. RESULTS: At rest, LF-HRV (sympathetic) was significantly increased in CFS compared to controls, while parasympathetic markers were significantly reduced (P = 0.006). Total DBP spectral power was increased (P = 0.0003) across all domains, with a shift towards sympathetic and away from parasympathetic SBPV (P = 0.05). On standing, overall SBPV response was significantly reduced with reductions in both sympathetic and parasympathetic components of SBPV (all P < 0.0001). Change in LF-DBP and relative balance of LF/HF DBP on standing differed between CFS and controls (P < 0.0001). Using the 85% sensitivity levels, we determined a threshold for three chosen resting BPV parameters of LF DBP >3.185, rest HF DBP >0.86, rest total DBP >7.05. Achieving all of these differentiated between CFS and controls with 77% sensitivity and 53% specificity. CONCLUSION: This study has shown that there are objectively measured abnormalities of blood pressure variability in CFS and that these abnormalities have the potential to be a bedside diagnostic tool.

Daily pattern of breathing in healthy young men.

Daily changes in the pulmonary function indices were examined in 30 healthy young men. The breathing pattern technique (Lungtest system, MES, Cracow) was used to measure daily changes in basic ventilatory parameters every 3 hours during a 24-hour period. The results revealed significant daily variables in VT (tidal volume), MV (minute ventilation), VT/TI (mean inspiratory flow), and the ratios of MV/P0. 1, (minute ventilation/mouth occlusion pressure) and P0.1/VT/TI. There was lack of significant variations in the other variables. The daily minima in the variables occurred during the usual sleep period at 2:00, 5:00 and also at 8:00 hours. The results of this study demonstrate that healthy adults have small, but significant, daily variations in some of the breathing parameters, although, overall, the breathing pattern remains relatively stable around the clock.

The role of cardiac and vascular components in blood pressure variability during voluntary apnea in snoring subjects.

The aim of this study was to evaluate the cardiovascular response to the activation of arterial chemoreceptors during voluntary apnea in snoring subjects. Fifty five men were enrolled in the study: 33 snorers and 22 non-snorers (control group). The majority of snorers were overweight and hypertensive. The experimental session consisted of 20 voluntary inspiratory apneas interspersed with 1 min free breathing periods, and 20 min recovery. The following parameters were recorded noninvasively: blood pressure, ECG, and arterial oxygen saturation. Data analysis was based on the Smietanowski procedure, written in the 4-th generation script language of MATLAB environment, which allows assessing the relative contribution of cardiac and vascular components to blood pressure variability. The results indicate that repetitive apneas led to significantly greater increases in blood pressure in the snorers. In this group, the domination of vascular influences during apnea periods reached 67 +/-2.0%, which was greater than the 56 +/-1.8% in the non-snorers (P<0.01). In contrast, the contribution of the cardiac component in the blood pressure response to apnea was greater in the non-snorers: 33 +/-3% vs. 20 +/-2% in the snorers (P<0.01). We conclude that activation of carotid chemoreceptors during voluntary apnea evokes a greater cardiovascular response in snorers, related to the reflex increase in total peripheral vascular resistance, and, consequently, a greater increase in blood pressure.

Effects of training on the ventilatory response to hypoxia.

The purpose of the present study was to examine the influence of systematical training on the ventilatory response to hypoxia. A rebreathing technique - progressive isocapnic hypoxia - was used to measure hypoxic chemoreflex reactivity. The ventilatory response was measured in a group of 22 world class adult kayakers (22.6 +/-1.9 yr), 16 young kayakers (17.8 +/-1.1 yr), and 38 control subjects (21.9 +/-1.9 yr). The ventilatory response to hypoxia - analyzed as the relationship (slope) MV/SaO(2) (minute ventilation/oxygen arterial blood saturation) - in the adult kayakers was significantly lower (-1.03 +/-0.28 L/min/%, P<0.01) compared with those in the control group (-1.81 +/-0.54 L/min/%) and the young kayakers (-1.54 +/-0.6 L/min/%; the difference between the latter two was insignificant). The following values of P(0.1)/SaO(2) (mouth occlusion pressure/oxygen arterial blood saturation) relationship were found for the investigated groups: adult kayakers (-0.20 +/-0.1 cm H/(2)O/%, P<0.05), young kayakers (-0.47 +/-0.1 cm H/(2)O/%, N.S.), control group (-0.48 +/-0.18 cm H(2)O/%). Correlation between the hypoxic ventilatory response and VO(2)max was significant in both groups of kayakers. These findings indicate that tolerance for hypoxia was elevated in the group of athletes compared with the control group. Hypoxic tolerance correlates with the duration of training.

Prevalence of sleep apnea syndrome in hemodialyzed patients with end-stage renal disease.

The majority of hemodialyzed patients suffer from sleep disturbances. In the present study the prevalence of sleep apnea syndrome in hemodialyzed patients with end-stage renal disease (ESRD-patients) was investigated by the survey, Epworth Sleepiness Scale (ESS), and polysomnography (PSG). Sixty-one patients: 24 women and 37 men were involved in the study. All subjects participated in the first part of the study consisting of the survey and ESS. The second and third parts consisted of nighttime PSG, performed the night after hemodialysis (17 patients) and between hemodialyses (11 patients). Eleven out of the 61 patients had the symptoms of sleep apnea and heavy daily sleepiness. Eleven subjects were involved in the double PSG study: after and between hemodialyses. Obstructive sleep apnea was found in 7 of those patients during both nights analyzed. Our results confirm the occurrence of sleep disorders in ESRD-patients. Hemodialysis does not change the prevalence of obstructive sleep apnea in chronic renal disease.

Improvement in the face/name association performance after three months of physical training in elderly women.

Several lines of evidence suggest that physical exercise not only influences the development of muscles, cardiovascular and respiratory systems, but also exerts a significant influence on the central nervous system. We examined the influence of strength and endurance training on cognitive performance in 33 healthy elderly volunteers (women, mean age 63.5 +/-4.5 yr) over a 3-month period of supervised training program. A control group consisted of 8 age-matched (mean age 66.3 +/-4.6) healthy volunteers who did not participate in any exercise training program. To evaluate the cognitive performance in our subjects we used two tests: face/name association test and Stroop test. The tests were applied shortly before and immediately after the training program. In the experimental group, a significant improvement in the association test performance, on average, from 71.6 +/-7.3% to 79.7 +/-7.2% (P<0.0001) was observed over the 3-month training period. There were no changes in the Stroop test results over the same time. Likewise, there were no changes in the control groups. Our data demonstrate that the training regime that is strictly followed over a relatively short period of time may improve the performance in associative memory tasks in elderly subjects. The study supports the notion that physical exercise influences cognitive performance and extend this notion to be valid for healthy elderly subjects.

Occurrence of obstructive sleep apnea in a group of shift worked police officers.

Shift work is an important source of health disturbances. Night work has a negative influence on some spheres: biological, working, social, and medical. Disturbances of sleeping, one group of manifestations of medical problems, can be considered as a cause of health deterioration. This study focuses on the occurrence of breathing disturbances during sleep in shift workers. Twenty one shift worked police officers (40-60 years old) were compared with an age-matched control group operating in the some environment. All subjects underwent overnight polysomnography. The polysomnographic investigation by shift workers was conducted after a day shift and normal night sleep, after an adaptational night in the sleep laboratory. Obstructive sleep apnea was found in 8 shift workers (38%) with AHI of 5.72-45.45 and in 8 control volunteers (38% of the studied group) with AHI of 5.00-25.24. All breathing parameters, as measured by polysomnography, did not differ between the two groups. Our results do not confirm the hypothesis that chronic irregular work hours promote the occurrence of obstructive sleep apnea in subjects aged 40-60 years.

Does night work favor sleep-related accidents in police officers?

Several studies of sleep-breathing physiology have suggested that sleep deprivation may worsen obstructive sleep apnea. The aim of the study was to determine the direct effect of night work on breathing variables during sleep in fast-rotating shift workers. Twenty one men - police officers, fast-rotating shift workers, underwent polysomnography on 2 occasions: under a normal sleeping condition after day work and after sleep deprivations after night work. Both sleep studies were conducted within 2 to 3 weeks of each other. Approximately half of the group was tested under control conditions (day work) first, with the remaining subjects tested under sleep deprivation conditions (night work) first. After a night shift the subjects did not show a significantly different apnea-hypopnea-index (AHI). However, night work significantly increased several breathing variables recorded during sleep after it: total duration of obstructive apneas (OA) during REM sleep, mean duration of OA during arousal, total duration of OA during NREM sleep, apnea index during arousal, mean length of OA during sleep period time, total duration of OA during sleep period time, mean length of OA during total sleep time, mean length of hypopnea during REM sleep, total duration of hypopnea during sleep period time and during total sleep time, maximal length of central apnea and OA, and total sleep time. Night work does not favor obstructive sleep apnea episodes during sleep, but worsens many an obstructive sleep apnea variable, as measured by polysomnography.

Age-related response of the genioglossus muscle EMG-activity to hypoxia in humans.

The prevalence of snoring and obstructive sleep apnea syndrome increases with age. Upper airway obstruction during sleep occurs when the dilator muscles are unable to overcome the negative pharyngeal pressure. The very important muscle dilator of the upper airway is the genioglossus muscle (GG). Our previous study showed an increase in GG-EMG activity during progressive hypoxia. In the present study a hypoxic increase in GG-EMG activity in response to hypoxia was investigated in two groups of 10 healthy subjects each: aged 29.1 +/- and aged 53.2 +/-2.3. The older humans showed reduced response of GG to hypoxia. We suggest that the biological aging process may be a risk factor for the obstructive sleep apnea syndrome.

Role of nose breathing in genioglossus muscle response to hypoxia in older and younger subjects.

Several studies showed that nasal airway is an active component of the respiratory system. Clinical data suggest that nasal obstruction causes episodes of obstructive apnea or hypopnea. In the present study, a possible influence of breathing through the nose on genioglossus muscle (GG, dilator of upper airway) reactivity to hypoxic activation was studied. Two groups of 20-30 years and 41-55 years old, 35 healthy subjects each, were investigated. The GG-EMG-activity was recorded and analyzed during progressive normocapnic hypoxia. The subjects breathed through the nose (N) or mouth (M) alone and through the nose and mouth (N&M). Significantly smaller increases in the GG-EMG-activity in response to hypoxia were observed during M breathing, as compared with N and M&N breathing, in both groups. The older subjects also showed a reduced response of GG-muscle to hypoxia, which was most pronounced during M breathing. We suggest that breathing through the nose activates the dilator muscle of upper airways, preventing apnea events.

[Physiologic rhythm of sleep and waking]. / Fizjologia rytmu snu i czuwania.

The sleep-wake cycle is one of the endogenous rhythm of the body that become entrained to the day/night cycle. Light serves as a Zeitgeber, a stimulus that entrains an endogenous rhythm to the circadian clock. A direct retinohypothalamic tract (RHT) conveyed information about light to the internal circadian pacemaker. The primary biological clock is located in the suprachiasmatic nucleus (SCN). The RHT may serve to couple the circadian system to the external light/dark cycle.

The carotid bodies of hypertensive/normotensive hybrid rats.

The carotid bodies of F1- and F2-hybrids of spontaneously hypertensive rats of the Okamoto-Aoki strain (SHR) and normotensive Wistar rats (NWR) were studied. Both the F1- and the F2-generation exhibited an elevated mean arterial blood pressure. In the F1-hybrids smaller carotid bodies and fewer intraglomic vascular changes, but higher mean arterial blood pressure than in the F2-hybrids were found. In both groups there was no correlation between carotid body size and the occurrence of intraglomic vessel alterations. In general, vascular changes were less developed than in age-matched SHR. It is concluded that in SHR/NWR F1- and F2-hybrids the development of carotid body enlargement is not only dependent on an elevated blood pressure or the presence of intraglomic pad-like vascular alterations.