Sex differences in awake ventilatory drive and abnormal breathing during sleep in eucapnic obesity

A retrospective study of the influence of obesity on polysomnography and cephalometric parameters in males with obstructive sleep apnea

OBJECTIVE

Evaluate the influence of obesity on the polysomnographic and cephalometric parameters in obstructive sleep apnea (OSA).

METHODS

Fifty records of male patients with OSA, containing information on dental, medical, polysomnographic, and cephalometric exams were selected. The degree of obesity was based on Body Mass Index (BMI). Group I comprised normal or overweight individuals (BMI ≤ 29.9 kg/m2), whereas Group II consisted of obese individuals (BMI ≥ 29.9 kg/m2).

RESULTS

BMI significantly correlated with apnea and hypopnea index (p < 0.0005), minimal oxyhemoglobin saturation (p < 0.0005), and two cephalometric variables (soft palate length, p = 0.01 and width, p = 0.01). Group II showed a significant correlation with the position of the hyoid bone (p = 0.02). Soft palate length and width significantly differed between groups (p = 0.014; 0.016).

CONCLUSION

Obese males present wider and longer soft palate dimensions, and patients with a greater BMI present a more inferiorly positioned hyoid bone.

Women at Altitude: Sex-Related Physiological Responses to Exercise in Hypoxia

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a limited number without analyzing sex-related differences. To address this gap, this comprehensive review conducted an extensive literature search to examine changes in physiological functions related to oxygen transport and consumption in hypoxic conditions. The review encompasses various aspects, including ventilatory responses, cardiovascular adjustments, hematological alterations, muscle metabolism shifts, and autonomic function modifications. Furthermore, it delves into the influence of sex hormones, which evolve throughout life, encompassing considerations related to the menstrual cycle and menopause. Among these physiological functions, the ventilatory response to exercise emerges as one of the most sex-sensitive factors that may modify reactions to hypoxia. While no significant sex-based differences were observed in cardiac hemodynamic changes during hypoxia, there is evidence of greater vascular reactivity in women, particularly at rest or when combined with exercise. Consequently, a diffusive mechanism appears to be implicated in sex-related variations in responses to hypoxia. Despite well-established sex disparities in hematological parameters, both acute and chronic hematological responses to hypoxia do not seem to differ significantly between sexes. However, it is important to note that these responses are sensitive to fluctuations in sex hormones, and further investigation is needed to elucidate the impact of the menstrual cycle and menopause on physiological responses to hypoxia.

Sex-differences in the sympathetic neurocirculatory responses to chemoreflex activation

Abstract

The purpose of this study was to determine whether there are sex differences in the cardiorespiratory and sympathetic neurocirculatory responses to central, peripheral, and combined central and peripheral chemoreflex activation. Ten women (29 ± 6 years, 22.8 ± 2.4 kg/m²: mean ± SD) and 10 men (30 ± 7 years, 24.8 ± 3.2 kg/m²) undertook randomized 5 min breathing trials of: room air (eucapnia), isocapnic hypoxia (10% oxygen (O₂); peripheral chemoreflex activation), hypercapnic hyperoxia (7% carbon dioxide (CO₂), 50% O₂; central chemoreflex activation) and hypercapnic hypoxia (7% CO₂, 10% O₂; central and peripheral chemoreflex activation). Control trials of isocapnic hyperoxia (peripheral chemoreflex inhibition) and hypocapnic hyperoxia (central and peripheral chemoreflex inhibition) were also included. Muscle sympathetic nerve activity (MSNA; microneurography), mean arterial pressure (MAP; finger photoplethysmography) and minute ventilation (V˙_E; pneumotachometer) were measured. Total MSNA (P = 1.000 and P = 0.616), MAP (P = 0.265) and V˙_E (P = 0.587 and P = 0.472) were not different in men and women during eucapnia and during isocapnic hypoxia. Women exhibited attenuated increases in V˙_E during hypercapnic hyperoxia (27.3 ± 6.3 vs. 39.5 ± 7.5 l/min, P < 0.0001) and hypercapnic hypoxia (40.9 ± 9.1 vs. 53.8 ± 13.3 l/min, P < 0.0001) compared with men. However, total MSNA responses were augmented in women (hypercapnic hyperoxia 378 ± 215 vs. 258 ± 107%, P = 0.017; hypercapnic hypoxia 607 ± 290 vs. 362 ± 268%, P < 0.0001). No sex differences in total MSNA, MAP or V˙_E were observed during isocapnic hyperoxia and hypocapnic hyperoxia. Our results indicate that young women have augmented sympathetic responses to central chemoreflex activation, which explains the augmented MSNA response to combined central and peripheral chemoreflex activation.

Key points

Sex differences in the control of breathing have been well studied, but whether there are differences in the sympathetic neurocirculatory responses to chemoreflex activation between healthy women and men is incompletely understood.

We observed that, compared with young men, young women displayed augmented increases in muscle sympathetic nerve activity during both hypercapnic hyperoxia (central chemoreflex activation) and hypercapnic hypoxia (central and peripheral chemoreflex activation) but had attenuated increases in minute ventilation.

In contrast, no sex differences were found in either muscle sympathetic nerve activity or minute ventilation responses to isocapnic hypoxia (peripheral chemoreceptor stimulation).

Young women have blunted ventilator, but augmented sympathetic responses, to central (hypercapnic hyperoxia) and combined central and peripheral chemoreflex activation (hypercapnic hypoxia), compared with young men. The possible causative association between the reduced ventilation and heightened sympathetic responses in young women awaits validation.

Breathing Re-Education and Phenotypes of Sleep Apnea: A Review

Four phenotypes of obstructive sleep apnea hypopnea syndrome (OSAHS) have been identified. Only one of these is anatomical. As such, anatomically based treatments for OSAHS may not fully resolve the condition. Equally, compliance and uptake of gold-standard treatments is inadequate. This has led to interest in novel therapies that provide the basis for personalized treatment protocols. This review examines each of the four phenotypes of OSAHS and explores how these could be targeted using breathing re-education from three dimensions of functional breathing: biochemical, biomechanical and resonant frequency. Breathing re-education and myofunctional therapy may be helpful for patients across all four phenotypes of OSAHS. More research is urgently needed to investigate the therapeutic benefits of restoring nasal breathing and functional breathing patterns across all three dimensions in order to provide a treatment approach that is tailored to the individual patient.

Sex differences in breathing

Breathing is a vital behavior that ensures both the adequate supply of oxygen and the elimination of CO₂, and it is influenced by many factors. Despite that most of the studies in respiratory physiology rely heavily on male subjects, there is much evidence to suggest that sex is an important factor in the respiratory control system, including the susceptibility for some diseases. These different respiratory responses in males and females may be related to the actions of sex hormones, especially in adulthood. These hormones affect neuromodulatory systems that influence the central medullary rhythm/pontine pattern generator and integrator, sensory inputs to the integrator and motor output to the respiratory muscles. In this article, we will first review the sex dependence on the prevalence of some respiratory-related diseases. Then, we will discuss the role of sex and gonadal hormones in respiratory control under resting conditions and during respiratory challenges, such as hypoxia and hypercapnia, and whether hormonal fluctuations during the estrous/menstrual cycle affect breathing control. We will then discuss the role of the locus coeruleus, a sexually dimorphic CO₂/pH-chemosensitive nucleus, on breathing regulation in males and females. Next, we will highlight the studies that exist regarding sex differences in respiratory control during development. Finally, the few existing studies regarding the influence of sex on breathing control in non-mammalian vertebrates will be discussed.

High-fat diet increases respiratory frequency and abdominal expiratory motor activity during hypercapnia

Breathing disorders are commonly observed in association with obesity. Here we tested whether high-fat diet (HFD) impairs the chemoreflex ventilatory response. Male Holtzman rats (300-320 g) were fed with standard chow diet (SD) or HFD for 12 weeks. Then, tidal volume (VT), respiratory frequency (fR) and pulmonary ventilation (VE) were determined in conscious rats during basal condition, hypercapnia (7% or 10% CO2) or hypoxia (7% O2). The mean arterial pressure (MAP), heart rate (HR) and baroreflex sensitivity were also evaluated in conscious rats. A group of anesthetized rats was used for the measurements of the activity of inspiratory (diaphragm) and expiratory (abdominal) muscles under the same gas conditions. Baseline fR, VT and VE were similar between SD and HFD rats. During hypercapnia, the increase of fR was exacerbated in conscious HFD rats (60 ± 3, vs. SD: 47 ± 3 Δ breaths.min-1, P < 0.05). In anesthetized rats, hypercapnia strongly increased abdominal muscle activity in HFD group (238 ± 27, vs. basal condition: 100 ± 0.3%; P < 0.05), without significant change in SD group (129 ± 2.1, vs. basal condition: 100 ± 0.8%; P = 0.34). The ventilatory responses to hypoxia were similar between groups. In conscious HFD rats, MAP and HR were elevated and the baroreflex function was impaired (P < 0.05). These data demonstrated that 12 weeks of HFD exaggerate the ventilatory response activated by hypercapnia. The mechanisms involved in these responses need more investigation in future studies.

Voluntary breath-holding duration in healthy subjects with obesity: Role of peripheral chemosensitivity to carbon dioxide

OBJECTIVE

The present study aimed to explore the peripheral chemoreflex sensitivity in healthy subjects with high body mass index (BMI).

METHODS

We studied 26 healthy men with obesity and 23 healthy men without obesity. All participants performed the breath-holding test in the morning, and the single-breath carbon dioxide (SB-CO₂) test on the next day.

RESULTS

The sensitivity of peripheral chemoreceptors to CO₂ did not differ between two groups (P = .47). In contrast, the duration of breath-holding was significantly lower in participants with elevated BMI (40.6 ± 10.5 s versus 47.2 ± 8.7 s; P < .05). In the multifactor regression model, only differences in waist-to-hip ratio (WHR) and SB-CO₂ remained statistically significant (R² for the model = 0.62, P < .001).

CONCLUSIONS

The sensitivity of peripheral chemoreflex to CO₂ was preserved in healthy men with obesity. The higher sensitivity of peripheral chemoreflex to CO₂ and higher WHR were associated with a decrease in the duration of voluntary apnea in subjects with obesity.

Increased body fat is associated with potentiation of blood pressure response to hypoxia in healthy men: relations with insulin and leptin

Background

Increased peripheral chemosensitivity (PChS) has been proposed as mechanism underlying obesity-related sympathoactivation, with insulin and/or leptin as possible mediators. However, human data on PChS in obesity are scarce. Therefore, we explored this issue in a sample of 41 healthy men aged 30–59 years, divided according to body fat percentage (fat %) into two groups: <25 and ≥25 %.

Methods

PChS was assessed using transient hypoxia method [respiratory (PChS-MV), heart rate (PChS-HR), and blood pressure (PChS-SBP) responses were calculated]. Baroreflex sensitivity (BRS-Seq) was assessed using sequence method. Fasting plasma insulin and leptin levels were measured. Homeostatic model assessment (HOMA) was used to assess insulin sensitivity/resistance.

Results

Individuals with ≥25 % body fat demonstrated increased PChS-SBP (p < 0.01), but unchanged PChS-MV and PChS-HR (both p > 0.4). PChS-SBP was related positively with anthropometric characteristics (e.g. waist circumference, fat %), plasma insulin and HOMA (all p < 0.05), and negatively with BRS-Seq (p = 0.001), but not with plasma leptin (p = 0.27).

Conclusions

In healthy men, overweight/obesity is accompanied by augmented blood pressure response from peripheral chemoreceptors, while respiratory and heart rate responses remain unaltered. Hyperinsulinaemia and insulin resistance (but not hyperleptinaemia) are associated with augmented pressure response from chemoreceptors.

Electronic supplementary material

The online version of this article (doi:10.1007/s10286-015-0338-2) contains supplementary material, which is available to authorized users.

Obesity: challenges to ventilatory control during exercise--a brief review

Obesity is a national health issue in the US. Among the many physiological changes induced by obesity, it also presents a unique challenge to ventilatory control during exercise due to increased metabolic demand of moving larger limbs, increased work of breathing due to extra weight on the chest wall, and changes in breathing mechanics. These challenges to ventilatory control in obesity can be inconspicuous or overt among obese adults but for the most part adaptation of ventilatory control during exercise in obesity appears remarkably unnoticed in the majority of obese people. In this brief review, the changes to ventilatory control required for maintaining normal ventilation during exercise will be examined, especially the interaction between respiratory neural drive and ventilation. Also, gaps in our current knowledge will be discussed.

Is mandatory screening for obstructive sleep apnea with polysomnography in all severely obese patients indicated?

PURPOSE

The study aims to assess the risk factors for the presence and severity of obstructive sleep apnea (OSA) among severely obese patients evaluated for bariatric surgery.

PATIENTS AND METHODS

Polysomnography recordings were performed in consecutive patients undergoing Roux-en-Y gastric bypass from January 2004 to January 2007. Sleep apnea was noted as present or absent and graded from mild to severe according to the apnea/hypopnea index. Patient gender, age, weight, height, body mass index, neck circumference, and waist circumference were recorded.

RESULTS

A total of 132 patients were included in the study group, and 85 patients had a confirmed diagnosis of OSA (64.4%). The prevalence of OSA was 55.7% in female and 77.4% in male. The prevalence of moderate or severe sleep apnea was higher in males (71.6%) than in females (31.6%). In OSA patients, body mass index (p = 0.020), neck circumference (p < 0.001), and age (p = 0.003) were higher as compared with obese patients without OSA, whereas no differences were found in waist circumference between groups. After multiple regression analysis, body mass index, age, and male gender were independent predictors of sleep apnea. In the female group, age greater than 49 years was the only significant predictor of moderate or severe OSA (odds ratio 5.42 (95% confidence interval 1.61-18.1); p = 0.006).

CONCLUSION

Males and females with age greater than 49 years are at greatest risk for OSA. Preoperative sleep studies should be mandatory in this group of severely obese patients.

The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis

The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.

Childhood obesity and obstructive sleep apnea syndrome

The increasing prevalence of obesity in children seems to be associated with an increased prevalence of obstructive sleep apnea syndrome (OSAS) in children. Possible pathophysiological mechanisms contributing to this association include the following: adenotonsillar hypertrophy due to increased somatic growth, increased critical airway closing pressure, altered chest wall mechanics, and abnormalities of ventilatory control. However, the details of these mechanisms and their interactions have not been elucidated. In addition, obesity and OSAS are both associated with metabolic syndrome, which is a constellation of features such as hypertension, insulin resistance, dyslipidemia, abdominal obesity, and prothrombotic and proinflammatory states. There is some evidence that OSAS may contribute to the progression of metabolic syndrome with a potential for significant morbidity. The treatment of OSAS in obese children has not been standardized. Adenotonsillectomy is considered the primary intervention followed by continuous positive airway pressure treatment if OSAS persists. Other methods such as oral appliances, surgery, positional therapy, and weight loss may be beneficial for individual subjects. The present review discusses these issues and suggests an approach to the management of obese children with snoring and possible OSAS.

Respiratory consequences of obesity--an overview

At the beginning of the 21st century obesity has become the leading chronic disease in the world. It is a major cause of morbidity mainly in the metabolic and cardiovascular areas. Moreover, it has progressively emerged as an important risk factor for respiratory diseases, a field that is often neglected. In this article, we reviewed the current understanding of the influence of obesity in adulthood on respiratory function, obstructive sleep apnoea-hypopnoea, obesity hypoventilation syndrome and asthma.

Gender differences on polysomnographic findings in Greek subjects with obstructive sleep apnea syndrome

BACKGROUND AND PURPOSE

Studies from North American clinics have reported that females with obstructive sleep apnea syndrome (OSAS) are about the same age as males but are heavier, have less severe apnea and make up a much smaller proportion of cases. We examined polysomnographic differences between Greek men and women with OSAS in order to study the influence of gender on clinical presentation and laboratory findings.

PATIENTS AND METHODS

This retrospective study included a cohort of 1,010 Greek patients (844 males, 166 females) diagnosed with OSAS by overnight polysomnography (PSG), who were referred to the Sleep Disorders Center of Evangelismos Hospital, Athens Medical School, University of Athens. All patients were studied over a period of three consecutive years, during which time clinical and polysomnography (PSG) findings were compared.

RESULTS

Body mass index (BMI) was similar in men and women with OSAS (BMI=31.6+/-5.5kg/m(2) in men versus BMI=32.5+/-8.1 (SD) kg/m(2) in women). Female patients were significantly older than male patients (56.9+/-10.6 versus 50.6+/-11.7 year, P=0.001). The mean apnea-hypopnea index (AHI) during total sleep time was higher in men than in women (42.4+/-28.2 versus 33.2+/-27.7 events/h, P<0.001). The AHI in non-rapid eye movement (NREM) sleep was higher in men than in women (42.9+/-28.9 versus 32.6+/-28.7 events/h, P<0.001), but in rapid eye movement (REM) sleep AHI was similar in men and women (36.0+/-23.3 versus 34.9+/-25.4 events/h). Forty percent of men had AHI-REM sleep >AHI-NREM compared to 62% of women, and the difference between REM and NREM-AHI was significantly less in men than in women (14.21+/-11.18 versus 19.76+/-13.43 events/h, P<0.001)). Several aspects of sleep were worse in women versus men: sleep efficiency index was lower (79.4+/-16.1% versus 85.1+/-12.5%, P<0.001); sleep onset latency (27.7+/-27.7 versus 17.9+/-18.1min, P<0.001), and REM onset latency (161.5+/-76.2 versus 145.7+/-71.4min, P<0.018) were longer; wake time after sleep onset (WASO) was also greater in women (42.6+/-46.5 versus 30.7+/-34.9min, P<0.003).

CONCLUSIONS

In Greek subjects with OSAS, there was no difference in BMI, and female patients were significantly older than male patients. OSAS was diagnosed in men five times more often than in women. AHI was greater in men than in women, but women are more likely than men to have a higher AHI in REM than NREM. Sleep quality is worse in female than in male patients.

Exaggerated respiratory chemosensitivity and association with level at 3568m in obesity

To investigate whether obesity is associated with alterations in respiratory chemosensitivity, we compared the ventilatory response to hypoxia (HVR) and hypercapnia (HCVR) in 9 obese men (BMI: 37.0+/-4.3 kg m(-2)) and 10 lean men (BMI: 25.8+/-4.8 kg m(-2)). HVR (DeltaVE, L min(-1) per DeltaSaO2, %) was measured by a progressive isocapnic hypoxia technique, and HCVR (DeltaVE/DeltaPETCO2, L min(-1)Torr(-1)) was measured by a progressive hypercapnic method. HCVR, was greater (p<0.001) in the obese men (2.68+/-0.78) than in the lean men (1.4+/-0.45) as was HVR (p<0.05) (1.26+/-0.65 versus 0.71+/-0.43, respectively). The difference (DeltaSaO2, 4.30+/-3.69 and 10.54+/-3.45 in the lean and obese men, respectively, p<0.01) between daytime (86+/-1 and 86+/-1%) and nighttime SaO2 (81+/-3 and 76+/-4%) at a simulated altitude of 3658 m was significantly (p<0.05) correlated with both HVR (r=0.51) and HCVR (r=0.48). These results suggest that chemosensitivity in mildly obese men is increased, not blunted. Furthermore, otherwise healthy, obese individuals have the potential for significant desaturation during sleep at high altitude possibly due to exaggerated sleep-disordered breathing.

Chemoreflex control of breathing during wakefulness in healthy men and women

This study used a modified CO(2) rebreathing procedure to examine the effect of gender on the chemoreflex control of breathing during wakefulness in healthy men (n = 14) and women (n = 14). Women were tested in the follicular phase of the menstrual cycle. During rebreathing trials, subjects hyperventilated to reduce the partial pressure of end-tidal CO(2) (Pet(CO(2))) below 25 Torr and were then switched to a rebreathing bag containing a normocapnic hypoxic or hyperoxic gas mixture. During the trial, Pet(CO(2)) increased, while O(2) was maintained at a constant level. The point at which ventilation began to rise as Pet(CO(2)) increased was identified as the ventilatory recruitment threshold (VRT). Ventilation below the VRT was measured, and the slope of the ventilatory response above the VRT was determined. Gender had no effect on the hyperoxic or hypoxic VRT for CO(2). Central chemoreflex sensitivity was significantly greater in men than women but not after correction for forced vital capacity. Measures of peripheral chemoreflex sensitivity were similar between genders. However, the slope of the tidal volume (Vt) response to hyperoxic and hypoxic CO(2) rebreathing (corrected and uncorrected) was greater in men than women, respectively. We conclude that central chemoreflex sensitivity is greater in men compared with women as reflected by differences in ventilatory (uncorrected) and Vt (corrected and uncorrected) responses to CO(2). However, gender has no significant effect on the central chemoreflex VRT for CO(2). The peripheral chemoreflex control of breathing during wakefulness is similar between men and women.

Gender, age and menopause effects on the prevalence and the characteristics of obstructive sleep apnea in obesity

BACKGROUND

In the 1970s and 80s it was believed that obstructive sleep apnea (OSA) was primarily a disease of men. The present study was addressed to evaluate the effect of gender and menopause on the prevalence and the characteristics of OSA and on anthropometric, clinical, respiratory and polysomnographic data in a population of obese individuals.

PATIENTS AND METHODS

A total of 230 obese subjects (BMI >/= 30 kg m-2), 148 women and 82 men, aged 16-75 years, were recruited and evaluated for general and anthropometric parameters, respiratory function, sleep-related symptoms and sleep disorders of breathing.

RESULTS

Respiratory disturbance index (RDI) and the prevalence of OSA were lower in women than in men (P < 0.001 and P < 0.001, respectively). Among subjects < 55 years, neck circumference, percentage of predicted normal neck circumference (PPNC), waist-to-hip ratio (WHR), PaCO2, RDI and the prevalence of OSA were lower in female subjects (P = 0.05, P < 0.05, P < 0.001, P < 0.01 and P < 0.01, respectively). BMI, neck circumference, PPNC, WHR, RDI and the prevalence of OSA were higher in postmenopausal compared with premenopausal women (P < 0.01, P < 0.01, P < 0.01, P < 0.01 and P < 0.01, respectively).

CONCLUSIONS

Our study demonstrates that (i) the male dominance regarding the prevalence and the severity of OSA disappears in men older than 55 years, and (ii) menopause seems to play a pivotal role in modulating both the presence and the degree of sleep disorder.

Sex steroid hormones and the neural control of breathing

We review evidence that sex steroid hormones including estrogen, progesterone and testosterone are involved in the central neural control of breathing. Sex hormones may exert their effects on respiratory motoneurons via neuromodulators, in particular, the serotonergic system. Recent studies have shown that levels of serotonin (5HT) in the hypoglossal and phrenic nuclei are greater in female than in male rats. Serotonin-dependent plasticity in hypoglossal and phrenic motor output also differs in male and female rats. Changing levels of gonadal hormones throughout the estrus cycle coincide with changing levels of 5HT in respiratory motor nuclei, and gonadectomy in male rats results in a decrease in 5HT-dependent plasticity in respiratory motor output. We speculate that sex steroid hormones are critically involved in adaptations in the neural control of breathing throughout life, and that decreasing levels of these hormones with increasing age may have a negative influence on the respiratory control system in response to challenge.

Gender differences in sleep apnea: the role of neck circumference

STUDY OBJECTIVES

To determine whether differences in sleep apnea severity between men and women referred to a sleep clinic are related to the differences in neck circumference (NC).

STUDY DESIGN

Case series.

SETTING

University hospital sleep disorders clinic.

PARTICIPANTS

A total of 3,942 patients (2,753 men and 1,189 women) referred to the sleep clinic.

MEASUREMENTS AND RESULTS

All patients underwent nocturnal polysomnography. NC was used as a surrogate measure of upper airway obesity. We found that sleep apnea, defined an the apnea/hypopnea index (AHI) > 10/h, was significantly more frequent (60% vs 32%, chi(2) < 0.0001) and severe (mean +/- SE, 25 +/- 26/h vs 12 +/- 19/h, p < 0.0001) in men than in women. Men had significantly larger NC than women, but the difference became much less pronounced when we normalized NC to body height (0.24 +/- 0.02 vs 0.23 +/- 0.03, p < 0.0001). Men had significantly higher AHI than women even after controlling for age, body mass index (BMI), and neck/height ratio (NHR); analysis of covariance showed that mean AHI was 24.4 +/- 0.4 in men vs 14.8 +/- 0.7 in women (p < 0.0001). This difference persisted even when we matched men and women for NHR and BMI. Finally, multiple regression analysis revealed the following: (1) NHR was the most significant predictor of AHI, accounting for 19% of the variability; and (2) the slope of AHI vs NHR was significantly higher in men than in women.

CONCLUSIONS

We conclude the following: (1) the frequency and severity of sleep apnea in the sleep clinic population is greater in men than women, and (2) factors other than NC, age, and BMI must contribute to these gender differences.

Effect of obesity and/or sleep apnea on chemosensitivity: differences between men and women

The purpose of this study was to identify if obesity or obstructive sleep apnea (OSA) influence hypercapnic response (HCR) and hypoxic response (HR) taking into account differences between gender. Data are expressed in % predicted based on reference values of our laboratory ('Respir. Physiol. 113 (1998) 157'). Obese women without OSA (n=117, body mass index (BMI) 43+/-8 kg/m(2)) demonstrated an increased ventilatory (VE) and occlusion pressure (P(0.1)) HCR and HR slope: VE HCR 113 (NS), VE HCR/vital capacity (VC) 126 (P<0.05), P(0.1) HCR 130 (P<0.05), VE HR 136 (P<0.05), VE HR/VC 154 (P<0.001) and P(0.1) HR 210 (P<0.001) % predicted. Obese women with OSA (n=34, BMI 42+/-9 kg/m(2)) presented similar increased values for HCR and even more increased values for HR than obese women without OSA matched for age, height and BMI: VE HR 155 (P=NS), VE HR/VC 205 (P<0.05) and P(0.1) HR 273 (P<0.05) % predicted. In obese men (without or with OSA) HCR and HR values were similar to our reference values.

Determinants of chronic hypercapnia in Japanese men with obstructive sleep apnea syndrome

STUDY OBJECTIVE

To identify the determinants of chronic hypercapnia (ie, PaCO(2), > or = 45 mm Hg) in men with obstructive sleep apnea syndrome (OSAS) without airflow obstruction.

DESIGN

An analysis was conducted of 143 male patients with OSAS, which had been diagnosed by polysomnography (PSG), who had been referred to a university hospital. Patients were classified as hypercapnic (ie, PaCO(2), > or = 45 mm Hg) and normocapnic (ie, PaCO(2), < 45 mm Hg), and obese (ie, body mass index [BMI], > or = 30 kg/m(2)) or nonobese (ie, BMI, < 30 kg/m(2)). Patients with airflow obstruction (ie, FEV(1)/FVC ratio, < 70%) were excluded from the study. Baseline clinical characteristics, pulmonary function, PSG data, and blood gas data were compared between hypercapnic and normocapnic patients. Correlations between PaCO(2) and several anthropometric, respiratory, and polysomnographic variables were determined by stepwise multiple regression analysis.

RESULTS

Fifty-five patients (38%) were hypercapnic. Hypercapnic patients were younger and heavier, and had more abnormalities on pulmonary and PSG testing. Stepwise multiple regression analysis revealed that the PaCO(2) level was influenced significantly by the mean level of arterial oxygen saturation (SaO(2)) during sleep and by the percent of vital capacity (%VC) (R(2) = 0.430; p < 0.0001), indicating that 43% of the total variance in the PaCO(2) could be explained by the mean SaO(2) and %VC in hypercapnic patients. In contrast, only 13% of the total variance in the PaCO(2) was accounted for by the mean SaO(2) and BMI in normocapnic patients (R(2) = 0.134; p = 0.0034). The mean SaO(2), %VC, and PaO(2) were selected as independent variables for predicting the PaCO(2) in obese patients. These variables explained 41% of the total variance in the PaCO(2) (R(2) = 0.407; p < 0.0001), whereas the mean SaO(2) only accounted for 13% of the total variance in PaCO(2) levels in nonobese patients (R(2) = 0.134; p = 0.0064).

CONCLUSION

Nocturnal desaturation and restrictive pulmonary impairment play major roles in determining the PaCO(2) in hypercapnic and obese OSAS patients without airflow obstruction.

Enhanced sympathetic and ventilatory responses to central chemoreflex activation in heart failure

BACKGROUND

Sympathetic activation and respiratory abnormalities may each be implicated in the pathophysiology of congestive heart failure (CHF). Chemoreflexes are an important mechanism regulating both sympathetic drive and breathing. We therefore tested the hypothesis that chemoreflex function is altered in CHF.

METHODS AND RESULTS

We compared ventilatory, sympathetic, heart rate, and blood pressure responses to hypoxia, hypercapnia, and the cold pressor test in 9 patients with CHF and 9 control subjects matched for age and body mass index. Baseline muscle sympathetic nerve activity (MSNA) was higher in the patients with CHF compared with control subjects (47+/-8 versus 23+/-3 bursts per minute, P<0.01). During hypercapnia, patients with CHF had greater increases in minute ventilation (6.7+/-1.4 versus 2.7+/-0.9 L/min, P=0.03) and heart rate (7.0+/-2.1 versus 0.6+/-1.2 bpm, P=0.02). Despite higher ventilation, which inhibits sympathetic activity, the MSNA increase in patients with CHF was also greater than that in control subjects (58+/-12% versus 21+/-9%, P=0.03). Ventilatory, autonomic, and blood pressure responses to hypoxia and the cold pressor test in CHF patients were not different from those in control subjects.

CONCLUSIONS

Chronic heart failure is characterized by a selective potentiation of ventilatory and sympathetic responses to central chemoreceptor activation by hypercapnia.

Human obesity is characterized by a selective potentiation of central chemoreflex sensitivity

The chemoreflexes are an important mechanism for regulation of both breathing and autonomic cardiovascular function. Obesity is associated with an increased risk of alveolar hypoventilation and carbon dioxide retention, suggesting that abnormalities in chemoreflex control mechanisms may be implicated. We tested the hypothesis that chemoreflex function is altered in obesity. We compared ventilatory, sympathetic, heart rate, and blood pressure responses to hypercapnia, hypoxia, and the cold pressor test in 14 obese subjects and 14 normal-weight subjects matched for age and gender. During hypercapnia, the increase in minute ventilation was significantly greater in obese subjects (7.0+/-0.3 L/min) than in normal-weight subjects (3.3+/-1.1 L/min; P=0.03). Despite higher minute ventilation during hypercapnia in obese subjects, the increase in muscle sympathetic nerve activity was similar in obese and normal-weight subjects. When the inhibitory influence of breathing during hypercapnia was eliminated by apnea, the increase in sympathetic nerve activity in obese subjects (99+/-16%) was greater than in normal-weight subjects (44+/-16%; P=0.02). The magnitude of the ventilatory and autonomic responses to hypoxia and the cold pressor test was similar in obese and normal-weight subjects. We conclude that chemoreflex responses to hypercapnia are potentiated in eucapnic obese subjects. In contrast, responses to hypoxia and to the excitatory cold pressor stimulus in obese subjects are similar to those in normal-weight subjects. Thus, obesity is characterized by selective potentiation of central chemoreflex sensitivity.

Determinants of the hypercapnic and hypoxic response in normal man

The purpose of this study was: (1) to identify the determinants of the hypercapnic (HCR) and hypoxic response (HR) in normal man; (2) to find out if they are dependent on the HR model used; and (3) to investigate if the occlusion pressure (P0.1), in contrast to the VE HCR and HR, is independent of gender, anthropometrical and lung functional indices. A total of 26 men (42.4+/-12.4 years) and 25 women (40.1+/-13.7 years) were studied. We found that men and women have similar P0.1 respiratory drives, but VE differs and is higher in men because of their larger vital capacity. For comparisons of the HCR or HR either the P0.1, or the VE HCR and HR normalized for VC or FEV1 should be used. With advanced age the VE HCR decreases in women. Especially for the HR, the identification of determinants (including age) is dependent on the HR model used.

Ventilatory response to hypoxia in rats: gender differences

The ventilatory response to hypoxia of adult conscious rats, measured during sleep as change in ventilation-oxygen consumption ratio (VE/VO2) while breathing 10% O2 for 15-30 min, was found to be approximately 23% larger in females (female) than in males (male, p < 0.001). Also arterial PCO2 during hypoxia decreased more in female. The gender difference occurred at all metabolic levels, and was not related to normoxic VE/VO2 or the hypometabolic response to hypoxia; it was solely due to greater hyperpnea in female. With hypoxia, changes in blood pressure, heart rate and body temperature were similar between male and female; hence, gender differences in baro- or thermal-stimuli were not a contributing factor. Hematocrit, hemoglobin, lung, heart and diaphragm mass/body weight were also similar, whereas respiratory system compliance was higher, and resistance lower, in female. Ovariectomy did not change the female response. In prepubertal rats the VE/VO2 hypoxic response was also larger in female (approximately 12%, p < 0.05). After prolonged (approximately 4 months) hypoxia, the gender difference in the response to acute hypoxia was no longer statistically significant. In conclusion, conscious adult female rats have a higher ventilatory response to hypoxia than male. The reason for the difference remains elusive, but is probably not due to ovarian hormones.

Body fat distribution and sleep apnea severity in women

The contribution of body fat distribution to sleep-disordered breathing in women has not been examined in detail (to our knowledge). Fifty women under 65 years of age were diagnosed as having obstructive sleep apnea (OSA) by all-night polysomnography in a 6-month period. Twenty-five women underwent body fat measurements of skin folds and circumferences. The 12 premenopausal and 13 postmenopausal women did not differ in regard to apnea hypopnea index (AHI), SaO2 nadir, body mass index (BMI), or anthropometric measurements. The AHI for these 25 patients was related to the severity of obesity assessed by triceps and subscapular skin folds, the sum of the skin folds, waist circumference, and BMI. The SaO2 nadir correlated with triceps and subscapular skin folds, the sum of the skin folds, and neck skin fold. Clinical features of this same group of 25 women were then compared with those of 45 men with OSA previously described by our laboratory. The women, despite similar age, had less severe OSA than the men (AHI of 34.4 +/- 5.4 vs 51.1 +/- 4.9, p < 0.05). Despite similar BMIs and waist circumference, the men had evidence of a greater degree of upper body obesity with a larger subscapular skin fold thickness, waist-hip ratio, and neck circumference. In addition, for a given degree of upper-body obesity, men had more severe sleep apnea. These findings may explain, at least in part, the greater severity of OSA in the men.

Breathing frequency in sleep related respiratory disturbances

In normal adults, breathing frequency (f) is highly reproducible within an individual ranging from 8 to 25 min-1; during sleep, f is known to change only minimally. This variable is rarely reported in studies of adults with various sleep related respiratory disturbances (SRRD). We occasionally observed a spectacular increase of f during sleep in patients with SRRD associated with hypopnea and 02 desaturation. We undertook a retrospective study of 650 consecutive all-night polysomnographic recordings, in order to evaluate how often such an increase in breathing frequency occurs and with which factors it is associated. We excluded patients with major respiratory failure. We found 16 patients (11 males; mean +/- SD, age: 45 +/- 13 yrs; body mass index (BMI): 44 +/- 11 kg/m2) with f > 25 min-1 during sleep (tachypneic group, T). We performed a one-for-one matching for sex, age and BMI between the T and a control (C) group (age: 45 +/- 12 yrs; BMI 44 +/- 10 kg/m2), with similar sleep disturbances but normal f during sleep. We compared the f in each vigilance state by averaging five measurements of f, each of one minute duration in a stable period. We observed that: C patients showed no significant change in f in any vigilance state; T patients showed a higher f already during wakefulness (p < 0.05) and f increased significantly in all sleep stages (< 0.01). We compared the two groups for many clinical and polysomnographic variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Snoring, hypertension, and the sleep apnea syndrome. An epidemiologic survey of middle-aged women

The lower limit of the prevalence of sleep apnea syndrome (SAS) was estimated among women 40 to 59 years old by a two-stage procedure. In the first stage 2,016 questionnaires were mailed. The response rate was 75.6 percent. Daytime sleepiness was reported by 8.2 percent, habitual snoring by 11.2 percent, and intermittent snoring by 21.7 percent. There were altogether 128 women described with systemic hypertension and these women were more than twice as often habitual snorers. Logistic multiple regression analyses showed almost a threefold increase in the predicted prevalence of hypertension among intermittent and habitual snorers compared with nonsnorers in the age group 40 to 49 years old and a 60 percent increase in the 50- to 59-year-old age group. In the second stage, a group of 97 women highly suspected of SAS were selected because of their habitual snoring and daytime sleepiness. Eventually, 35 of these came for night studies and 14 were found to have SAS. Among the 35 women, 12 were hypertensive and nine of these had SAS. We estimated the lower limit of the prevalence of SAS to be 2.5 percent for women 40 to 59 years old. It is concluded that SAS is a relatively common occurrence among women, especially postmenopausal ones, and it is strongly related to hypertension.

Progesterone therapy for sleep apnea syndrome evaluated by occlusion pressure responses to exogenous loading

We investigated the mechanisms of the beneficial effect derived from progesterone therapy for sleep apnea syndrome (SAS). Nine patients with SAS were treated for 7 days with chlormadinone acetate (CMA), a respiratory stimulant known to increase not only CO2 and hypoxic chemosensitivity but also respiratory drive response for ventilatory loading. They were examined as to sleep events and ventilatory control during wakefulness before and during CMA treatment. Apnea-hypopnea index was significantly reduced from 51.1 +/- 5.7 to 43.6 +/- 8.1 episodes/h (p less than 0.05). The ratio of desaturation time with more than 4% SaO2 fall to total sleep time was diminished in seven of nine patients, and its mean value decreased from 44.9 +/- 8.6 to 28.7 +/- 8.1% (p less than 0.05). Both hypercapnic ventilatory response (HCVR) and load response during wakefulness were significantly increased, although isocapnic hypoxic ventilatory response (HVR) was not significantly enhanced by CMA. The degree of augmentation in awake load response as well as in HCVR was positively correlated with that of improvement in sleep-disordered breathing. Moreover, patients who did not show amelioration in oxygen desaturation were found to be incapable of increasing load response despite increased HCVR. We conclude that CMA therapy for sleep apnea syndrome is effective in the patients whose load response as well as respiratory control activity are augmented during wakefulness.