Resetting the baroreflex during snoring: Role of resistive loading and intra-thoracic pressure

Baroreflex sensitivity (BRS) is reduced during snoring in humans and animal models. We utilised our rabbit model to examine the contribution of increased upper airway resistance to baroreflex resetting during snoring, by comparing BRS and baroreflex operating point (OP) values during IS to those obtained during tracheostomised breathing through an external resistive load (RL) titrated to match IS levels of peak inspiratory pleural pressure (Ppl). During both IS and RL, BRS decreased by 45% and 49%. There was a linear relationship between the change in Ppl and the decrease in BRS, which was similar for IS and RL. During both RL and IS, there was a shift in OP driven by ～16% increase in HR and no change in arterial pressure. Snoring related depression of BRS is likely mediated via a HR driven change in OP, which itself may be the outcome of negative intra-thoracic pressure mediated effects on right atrial wall stretch reflex control of heart rate.     

Near-infrared spectroscopy determined brain and muscle oxygenation during exercise with normal and resistive breathing

To elevate effects of carbon dioxide (CO2) retention by way of an increased respiratory load during submaximal exercise (150 W), the concentration changes of oxy- (DeltaHbO2) and deoxy-haemoglobin (DeltaHb) of active muscles and the brain were determined by near-infrared spectroscopy (NIRS) in eight healthy males. During exercise, pulmonary ventilation increased to 33 (28-40) L min-1 (median with range) with no effect of a moderate breathing resistance (reduction of the pneumotach diameter from 30 to 14 and 10 mm). The end-tidal CO2 pressure (PETCO2) increased from 45 (42-48) to 48 (46-58) mmHg with a reduction of only 1% in the arterial haemoglobin O2 saturation (SaO2). During control exercise (normal breathing resistance), muscle and brain DeltaHbO2 were not different from the resting levels, and only the leg muscle DeltaHb increased (4 (-2-10) microM, P < 0.05). Moderate resistive breathing increased DeltaHbO2 of the intercostal and vastus lateralis muscles to 6 +/- (-5-14) and 1 (-7-9) microM(P < 0.05), respectively, while muscle DeltaHb was not affected. Cerebral DeltaHbO2 and DeltaHb became elevated to 6 (1-15) and 1 (-1-6) microM by resistive breathing (P < 0.05). Resistive breathing caused an increased concentration of oxygenated haemoglobin in active muscles and in the brain. The results indicate that CO2 influences blood flow to active skeletal muscle although its effect appears to be smaller than for the brain.     

Hyperoxia-induced alterations in cardiovascular function and autonomic control during return to normoxic breathing

Hyperoxia causes hemodynamic alterations. We hypothesized that cardiovascular and autonomic control changes last beyond the end of hyperoxic period into normoxia. Ten healthy volunteers were randomized to breathe either medical air or 100% oxygen for 45 min in a double-blind study design. Measurements were performed before (baseline) and during gas exposure, and then 10, 30, 60, and 90 min after gas exposure. Hemodynamic changes were studied by Doppler echocardiography. Changes in cardiac and vasomotor autonomic control were evaluated through changes in spectral power of heart rate variability and blood pressure variability. Cardiac baroreflex sensitivity was assessed by the sequence method. Hyperoxia significantly decreased heart rate and increased the high frequency power of heart rate variability, suggesting a chemoreflex increase in vagal activity since the slope of cardiac baroreflex was significantly decreased during hyperoxia. Hyperoxia increased significantly the systemic vascular resistances and decreased the low frequency power of blood pressure variability, suggesting that hyperoxic vasoconstriction was not supported by an increase in vascular sympathetic stimulation. These changes lasted for 10 min after hyperoxia (p < 0.05). After the end of hyperoxic exposure, the shift of the power spectral distribution of heart rate variability toward a pattern of increased cardiac sympathetic activity lasted for 30 min (p < 0.05), reflecting a resuming of baseline autonomic balance. Cardiac output and stroke volume were significantly decreased during hyperoxia and returned to baseline values (10 min) later than heart rate. In conclusion, hyperoxia effects continue during return to normoxic breathing, but cardiac and vascular parameters followed different time courses of recovery.     

Near‐infrared spectroscopy determined brain and muscle oxygenation during exercise with normal and resistive breathing

To elevate effects of carbon dioxide (CO₂) retention by way of an increased respiratory load during submaximal exercise (150 W), the concentration changes of oxy‐ (ΔHbO₂) and deoxy‐haemoglobin (ΔHb) of active muscles and the brain were determined by near‐infrared spectroscopy (NIRS) in eight healthy males. During exercise, pulmonary ventilation increased to 33 (28–40) L min^–1 (median with range) with no effect of a moderate breathing resistance (reduction of the pneumotach diameter from 30 to 14 and 10 mm). The end‐tidal CO₂ pressure (P_ETCO ₂) increased from 45 (42–48) to 48 (46–58) mmHg with a reduction of only 1% in the arterial haemoglobin O₂ saturation (S_aO ₂). During control exercise (normal breathing resistance), muscle and brain ΔHbO₂ were not different from the resting levels, and only the leg muscle ΔHb increased (4 (–2–10) μM , P < 0.05). Moderate resistive breathing increased ΔHbO₂ of the intercostal and vastus lateralis muscles to 6 ± (–5–14) and 1 (–7–9) μM (P < 0.05), respectively, while muscle ΔHb was not affected. Cerebral ΔHbO₂ and ΔHb became elevated to 6 (1–15) and 1 (–1–6) μM by resistive breathing (P < 0.05). Resistive breathing caused an increased concentration of oxygenated haemoglobin in active muscles and in the brain. The results indicate that CO₂ influences blood flow to active skeletal muscle although its effect appears to be smaller than for the brain.     

The effect of resistive breathing on leg muscle oxygenation using near-infrared spectroscopy during exercise in men

The effect of added respiratory work on leg muscle oxygenation during constant-load cycle ergometry was examined in six healthy adults. Exercise was initiated from a baseline of 20 W and increased to a power output corresponding to 90% of the estimated lactate threshold (moderate exercise) and to a power output yielding a tolerance limit of 11.8 min (+/- 1.4, S.D.) (heavy exercise). Ventilation and pulmonary gas exchange were measured breath-by-breath. Profiles of leg muscle oxygenation were determined throughout the protocol using near-infrared (NIR) spectroscopy (Hamamatsu NIRO 500) with optodes aligned midway along the vastus lateralis of the dominant leg. Four conditions were tested: (i) control (Con) where the subjects breathed spontaneously throughout, (ii) controlled breathing (Con Br) where breathing frequency and tidal volume were matched to the Con profile, (iii) increased work of breathing (Resist Br) in which a resistance of 7 cmH2O l(-1) s(-1) was inserted into the mouthpiece assembly, and (iv) partial leg blood flow occlusion (Leg Occl), where muscle perfusion was reduced by inflating a pressure cuff (approximately 90 mmHg) around the upper right thigh. During Resist Br and Leg Occl, subjects controlled their breathing pattern to reproduce the ventilatory profile of Con. An approximately 3 min period with respiratory resistance or pressure cuff was introduced approximately 4 min after exercise onset. NIR spectroscopy data for reduced haemoglobin-myoglobin (delta[Hb]) were extracted from the continuous display at specific times prior to, during and after removal of the resistance or pressure cuff. While the delta[Hb] increased during moderate- and heavy-intensity exercise, there was no additional increase in delta[Hb] with Resist Br. In contrast, delta[Hb] increased further with Leg Occl, reflecting increased muscle O2 extraction during the period of reduced muscle blood flow. In conclusion, increasing the work of breathing did not increase leg muscle deoxygenation during heavy exercise. Assuming that leg muscle O2 consumption did not decrease, this implies that leg blood flow was not reduced consequent to a redistribution of flow away from the working leg muscle.     

Subjective ratings of prolonged inspiratory resistive loaded breathing in males and females

Dyspnea and fear of suffocation are burdensome to patients with respiratory disease. Inspiratory resistive loads offer an experimental respiratory stimulus to quantify the discriminative domain of respiratory perception. Resistive (R) load magnitude estimation (ME) and subjective ratings were measured over sustained multiple breaths in healthy subjects. There was no significant group difference between the ME for Breath 1 and 20 for small R loads, but a significant gender difference for large R loads. Subjective responses of fear, fear of suffocation, displeasure, chest pressure, faintness, dizziness, fear of losing control, trembling, and tingling were significantly greater for females. These results demonstrate that ME of large resistive sustained loads elicits nonsignificant increases in ME in females, but a significant decrease in ME for males. The maintenance of ME in females co‐occurs with increased aversive processing relative to males.     

Cardiorespiratory synchronization during Zen meditation

The impact of meditation on cardiorespiratory synchronization with respect to breathing oscillations and the modulations of heart rate induced by respiration (respiratory sinus arrhythmia, RSA) was investigated in this study. Four different exercises (spontaneous breathing, mental task, Zen meditation, and Kinhin meditation) were consecutively performed by nine subjects mainly without any experience in meditation. An electrocardiogram and a respiratory trace were recorded simultaneously. On this basis the degree of cardiorespiratory synchronization was quantified by a technique which has been adopted from the analysis of weakly coupled chaotic oscillators. Both types of meditation showed a high degree of synchronization, whereas heartbeat and respiration were hardly synchronized during spontaneous breathing. During the mental task exercise the extent of synchronization was slightly higher than during spontaneous breathing. These results were largely determined by the breathing frequency because the two types of meditation induce low breathing frequencies which led to a pronounced and in-phase RSA. During the meditation the low breathing frequencies led to a decrease in the high frequency of heart rate variability, whereas the low frequency and the extent of RSA increased. The heart rate primarily reflected the degree of physical effort. The high degree of cardiorespiratory synchronization during meditation in unexperienced meditators suggests that the physiological implications of meditation does not require prior experience in meditation.     

Function of scalene muscles under conditions of quiet breathing and inspiratory resistive load

Low-threshold slow motor units in feline scalene muscle generated spontaneous discharges (6–8 imp/sec) during resting ventilation, which were independent of the respiration cycle. Under conditions of resistive load, activity of these motor units and its electromyographic pattern changed from tonic towards phasic type, synchronized with the inspiration phase. Removal of the load restored the initial pattern of activity. Clear dependency of activity transformations on respiratory load implies a functional modulation of respiratory neural drive to the scalene muscles and the role of these muscles in compensation of inspiratory load. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 12, pp. 623–626, December 1999     

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand‐alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.     

Sleep disordered breathing (SDB) experiences associated with snoring in adult Nigerians

Background

Snorers often experience symptoms of sleep disordered breathing (SDB) which is largely undiagnosed in the population. Information on SDB experiences is needed to target high-risk individuals that may benefit from treatment of snoring.

Objective

This study compares the experience of the nighttime and daytime symptoms of SDB of habitual snorers with that of non-habitually snoring adult subjects in a tertiary health facility in Nigeria.

Methods

A cross-sectional, comparative, hospital based study was conducted. Berlin questionnaire was administered to consecutive adult patients (subjects) attending ENT Clinic of OOUTH, Sagamu, Nigeria. Based on the responses to their experience of snoring, the subjects were categorized as habitual snorers or non-habitual snorers. General physical examinations with emphases on the nose, throat and neck were performed on the subjects. The experiences of nighttime and daytime symptoms of SDB were recorded and those of habitual snorers compared to non-habitual snorers.

Results

One hundred and ninety- five subjects participated in the study. M:F =1.3:1. Overall prevalence of snoring was 37.9% and habitual snoring was 18.5%. Habitual snoring was significantly associated with age, marital status and obesity (BMI>=30.0). There were statistically significant increased odds of experiencing the nighttime and daytime symptoms of SDB in habitual snorers compared to non-habitual snorers.

Conclusion

Adults that snore habitually had significantly more nighttime and daytime symptoms of SDB compared to those who do not snore habitually. Habitual snoring predisposes adult subjects to experiencing symptoms of SDB.     

Stress cardiovascular/autonomic interactions in mice

Studies evaluated the role of the autonomic nervous system in the cardiovascular response to stress using radiotelemetric blood pressure (BP) recording coupled with autoregressive spectral analysis. Conscious male C57/BL6 mice with carotid arterial telemetric catheters were exposed to acute episodes of shaker stress before and after administration of cholinergic, beta1-adrenergic and alpha1-adrenergic receptor antagonists. Pulse interval (PI) and systolic arterial pressure (SAP) were analyzed for variance and the low frequency (LF: 0.1-1.0 Hz) and high frequency (HF: 1-5 Hz) spectral components. Stress (5 min) increased BP and heart rate (HR) as well as PI and SAP variability. PI variance increased from 41+/-6 to 75+/-14 ms2 while SAP variance increased from 25+/-5 to 55+/-9 mm Hg2. Autonomic blockade had specific effects on stress-induced changes in PI and SAP and their respective variability. Atropine reduced the tachycardia and abolished the increase in PI variance and its LF component. Data documents that in mice the cholinergic system is fundamental for the maintenance of HR variability. Atropine had no effects on the BP responses, either the increase in SAP or the variance associated with stress. Atenolol blocked the increase in PI and SAP variability induced by stress. Prazosin reduced the tachycardia produced by stress and blocked the increase in PI (only LF) and SAP variability. Using quantitative spectral analysis of telemetrically collected BP data in mice along with pharmacological antagonism, we were able to accurately determine the role of autonomic input in the mediation of the stress response. Data verify the role of sympathetic/parasympathetic balance in stress-induced changes in HR, BP and indices of variance.     

Cardiorespiratory effects of nicotine exposure during development

Exposure to tobacco smoke is a major risk factor for the sudden infant death syndrome. Nicotine is thought to be the ingredient in tobacco smoke that is responsible for a multitude of cardiorespiratory effects during development, and pre- rather than postnatal exposure is considered to be most detrimental. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and developmental exposure produces structural changes as well as alterations in neuroregulation. Abnormalities have been described in sympathicovagal balance, arousal threshold and latency, breathing pattern at rest and apnea frequency, ventilatory response to hyperoxia or hypoxia, heart rate regulation and ability to autoresuscitate during severe hypoxia. This review discusses studies performed on infants of smoking mothers and nicotine-exposed animals yielding varying and sometimes inconsistent results that may be due to differences in experimental design, species and the dose of exposure. Taken together however, developmental nicotine exposure appears to induce vulnerability during hypoxia and a potential inability to survive severe asphyxia.     

Cardiorespiratory dynamics during sinusoidal and impulse exercise in man

Dynamic characteristics of ventilation, cardiac output, and gas exchange during sinusoidally varying work rates for the periods from 1 to 12 min and impulse work rate with a duration of 10 sec were studied on five healthy men in an upright position. Changes in work rate were given by controlling externally the electromagnetic braking system of a bicycle ergometer. Stroke volume, heart rate, and cardiac output during exercise were determined continuously by using an automated impedance cardiograph. Breath by breath determination in minute ventilation, respiratory frequency, tidal volume, oxygen consumption, carbon dioxide output, end-tidal pressures of oxygen and carbon dioxide, and gas exchange ratio were conducted. From these and steady-state response data amplitude and phase relations between each variable and the input work loads were obtained utilizing the frequency analysis techniques. The response characteristics to sinusoidal stimuli were well represented by first-order models with time constants for VE, VCO2, VO2, and Q averaging 75, 67, 52, and 36 sec, respectively. The kinetics of HR closely resembled that of Q. There was a close link between both the dynamics of VE and VCO2. On the other hand, the responses to impulse stimuli were better described by second-order models in which fast and slow response components were connected in parallel. However, the contribution of the fast component to total response was small. Although this response may support in its form the neuro-humoral concept to explain exercise hyperpnea, a tight linkage was observed between VE and VCO2 responses to impulse stimuli. Thus, hyperpnea during the unsteady-state of exercise may be explained by the cardiodynamic hypothesis.     

Oronasal breathing during exercise

The shift from nasal to oronasal breathing (ONBS) has been observed on 73 subjects with two independent methods. A first group of 63 subjects exercising on a bicycle ergometer at increasing work load (98–196 W) has been observed. On 35 subjects the highest value of ventilation attained with nasal breathing was 40.2±9.41 · min^–1 S.D. Ten subjects breathed through the mouth at all loads, while 5 never opened the mouth. On 13 subjects it was not possible to make reliable measurements. On a second group of 10 subjects utilizing a different techniques which did not need a face mask, the ventilation at which one changes the pattern of breathing was found to be 44.2±13.51·min^–1 S.D. On the same subjects nasal resistance did not show any correlation with ONBS. It is concluded that ONBS is not solely determined by nasal resistance, though an indirect effect due to hypoventilation and hence to changes in alveolar air composition cannot be ruled out. It is likely that ONBS is also influenced by psychological factors.     

High‐altitude hypoxia and periodic breathing during sleep: gender‐related differences

High‐altitude exposure is characterized by the appearance of periodic breathing during sleep. Only limited evidence is available, however, on the presence of gender‐related differences in this breathing pattern. In 37 healthy subjects, 23 male and 14 female, we performed nocturnal cardio‐respiratory monitoring in the following conditions: (1) sea level; (2) first/second night at an altitude of 3400 m; (3) first/second night at an altitude of 5400 m and after a 10 day sojourn at 5400 m. At sea level, a normal breathing pattern was observed in all subjects throughout the night. At 3400 m the apnea–hypopnea index was 40.3 ± 33.0 in males (central apneas 77.6%, central hypopneas 22.4%) and 2.4 ± 2.8 in females (central apneas 58.2%, central hypopneas 41.8%; P < 0.01). During the first recording at 5400 m, the apnea–hypopnea index was 87.5 ± 35.7 in males (central apneas 60.0%, central hypopneas 40.0%) and 41.1 ± 44.0 in females (central apneas 73.2%, central hypopneas 26.8%; P < 0.01), again with a higher frequency of central events in males as seen at lower altitude. Similar results were observed after 10 days. With increasing altitude, there was also a progressive reduction in respiratory cycle length during central apneas in males (26.9 ± 3.4 s at 3400 m and 22.6 ± 3.7 s at 5400 m). Females, who displayed a significant number of central apneas only at the highest reached altitude, were characterized by longer cycle length than males at similar altitude (30.1 ± 5.8 s at 5400 m). In conclusion, at high altitude, nocturnal periodic breathing affects males more than females. Females started to present a significant number of central sleep apneas only at the highest reached altitude. After 10 days at 5400 m gender differences in the apnea–hypopnea index similar to those observed after acute exposure were still observed, accompanied by differences in respiratory cycle length.     

Spontaneous autonomic activity as related to psychopathy

Spontaneous fluctuations and levels in skin conductance and finger pulse volume recordings were studied in criminal subjects during three experimental periods, before, during and after a series of auditory stimuli, and related to psychopathy as estimated by scores in the Gough delinquency scale (De). The sample was subdivided into two groups, containing subjects with scores above (HD) and below (LD) the median in the De scale. Analyses of variance yielded significant group x period interaction effects for skin conductance fluctuation and level measures. The more psychopathic group (HD) had a lower number of skin conductance fluctuations in stimulation and post-stimulation periods, and had lower levels, decreasing over periods. No differences were obtained in the pulse volume measurements. The lower skin conductance reactivity in the more psychopathic subjects was discussed in terms of lower cortical arousal, and the implications for the interpretation of skin conductance fluctuations were analysed.     

Affects and autonomic cardiac reactivity during experimentally induced stress as related to precursors of insulin resistance syndrome

This study examined the association of insulin resistance syndrome (IRS) precursors with state affects and autonomic reactivity in randomly selected healthy young adults. It was asked whether IRS precursors are able to predict a person’s mental and physiological coping with acute stress over an 11-year follow-up period. IRS parameters were serum insulin, high-density lipoprotein cholesterol, triglycerides, systolic blood pressure, body-mass index, and subscapular skinfold thickness. In the psychophysiological experiment, state affects and cardiac responses (heart rate, respiratory sinus arrhythmia, and pre-ejection period) were measured during different challenges. The main result was that IRS precursors predicted high levels of negative emotions during the challenges; IRS accounted for 19% of the variance in tiredness. IRS was unrelated to cardiac reactivity. Mechanisms underlying the associations found are discussed.