The rate and depth of breathing in new-born infants in different sleep states

1. Ventilation was recorded on ten male and ten female healthy full-term infants during the first week after delivery, using a trunk plethysmograph. Tidal volume (V(T)), respiration rate (f) and pulmonary ventilation (V) for each respiratory cycle were measured during periods of rapid eye movement sleep (REM) and during quiet sleep when eye movements were absent (NREM).2. It was found that mean instantaneous V and f were significantly higher in all infants during REM than during NREM sleep, while mean V(T) was either unchanged or showed a decrease. In addition, there was significantly greater variation in instantaneous V, V(T) and f during REM as compared with NREM sleep.3. Positive correlations were found in most infants in both sleep states between individual values of V(T) and the duration of the respiratory cycle (T).4. Periodic changes in T were found in all infants during both sleep states; these periodicities may reflect the behaviour of respiratory control mechanisms operating over a longer time span than the individual respiratory cycle.     

Respiratory muscle training reduces the work of breathing at depth

Resistance respiratory muscle training (RRMT) increases respiratory muscle and swimming performance at depths down to 17 msw. It is unknown if RRMT improves swimming performance at greater depths and if the improvements are associated with a reduced work of breathing (WOB), altered respiratory mechanics and/or improved respiratory muscle performance. Eight male subjects (30.3 ± 6.0 years) were tested swimming underwater in a hyperbaric chamber at 37 m of depth against a pre-determined load (70% [(V)dot]_{textO 2} dot{V}_{{{text{O}}_{ 2} }} ) until exhausted. End expiratory lung volume (EELV) was determined by subtracting inspiratory capacity from total lung capacity throughout the swims. The mechanical WOB on the lung was calculated as the integrated product of the transpulmonary pressure and ventilatory flow. Maximal expiratory (P _EMAX) and inspiratory pressures (P _IMAX) were measured pre- and post-RRMT. RRMT was performed every 30 s against spring loaded inspiratory and expiratory valves 30 min/day, 5 days/week, for 4 weeks. RRMT increased P _IMAX and P _EMAX by 40% (110 ± 11 cmH₂O (SD) vs. 155 ± 22, p < 0.001) and 30% (148 ± 33 cmH₂O vs. 192 ± 49, p < 0.001), respectively, respiratory endurance by 75% (19.7 ± 15.4 min vs. 34.4 ± 27.3, p = 0.010), and swimming endurance by 87% (26.4 ± 9.7 min vs. 49.4 ± 21.6, p = 0.004). The longer swimming time was associated with reduced [(V)dot]_textE dot{V}_{text{E}} and [(V)dot]_textA dot{V}_{text{A}} (p < 0.001), f _b (p < 0.001), [(V)dot]_textCO2 dot{V}_{{{text{CO}}_{2} }} (p < 0.001) and WOB (p < 0.001). There were no changes in EELV post-RRMT. These results suggest the improved exercise performance post-RRMT was associated with stronger respiratory muscles, a decreased f _b, and a reduced WOB.     

Heart rate response to breathing: dependency upon breathing pattern

Heart rate responses to stepwise and periodic changes in lung volume were studied in seven young healthy males. Stepwise inspiration and expiration both resulted in an increase in heart rate followed by a rapid decrease in heart rate. The fastest heart rate was reached in 1.6 +/- 0.5 s and in 3.6 +/- 1.4 s in response to inspiration and expiration, respectively (P less than 0.01). The slowest heart rate was reached in 4.8 +/- 1.0 s and in 7.6 +/- 1.9 s in response to inspiration and expiration, respectively (P less than 0.01). Following this biphasic change the heart rate returned to a steady level. The difference between the fastest and the slowest heart rates was significantly larger in response to inspiration (21.7 +/- 7.3 beats per minute) than in response to expiration (12.0 +/- 7.3 beats per minute; P less than 0.01). Periodic changes in lung volume were performed with frequencies from 3.0 to 12.0 respirations per minute (r.p.m.). The changes in heart rate showed a constant amplitude in the frequency range below 5.5 r.p.m. Maximal heart rate changes were found at frequencies of 5.5 to 7.0 r.p.m. Changes in heart rate decreased in a linear manner on a log-log scale in the frequency range above 7.0 r.p.m. The relation between frequency and changes in heart rate is explained by interference between the transient changes in heart rate induced both by inspiration and by expiration. It is concluded that if heart rate changes in response to periodic changes in lung volume are to be used as a measure of vagal function a number of factors have to be taken into consideration and to simplify the analysis of heart rate responses to breathing we recommend, instead, the use of the transient changes in heart rate induced by stepwise changes in lung volume.     

Effects of maternal breathing rate, psychiatric status, and cortisol on fetal heart rate

Women's experiences during pregnancy are predictive of variation in neurobehavioral profiles in their children. Few studies have assessed these relationships during the prenatal period. In 113 women in the 36^th –38^th gestational week (mean age 26.3 ± 5.4 years), electrocardiogram, blood pressure, respiration, salivary cortisol, and fetal heart rate (HR) were measured during baseline, a psychological challenge (Stroop color–word matching task), and a standardized paced breathing protocol. Subjects underwent the Structured Clinical Interview for DSM‐IV prior to testing and were grouped as: depressed, co–morbid for depression and anxiety, anxiety disorder only, and control. There was a significant main effect of maternal diagnostic group on fetal HR only during the Stroop task: fetuses of women in the co–morbid group had a greater HR increase compared to controls (p < .05). Overall, fetuses showed robust increases in HR during paced breathing (p < .0001), and there was no significant difference by maternal diagnosis. For both tasks, changes in fetal HR were independent of women's concurrent cardiorespiratory activity. Finally, although cortisol was higher in the co‐morbid group (p < .05), across all participants, there was a trend for maternal baseline cortisol to be positively associated with average fetal HR (p = .06). These findings indicate that variation in fetal HR reactivity—an index of emerging regulatory capacities—is likely influenced by multiple acute and chronic factors associated with women's psychobiology. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53:221–233, 2011.     

Mechanical factors in breathing pattern regulation in humans

The adult human breathing pattern is a complex product of neural, humoral, and perceptual factors, each of which is influenced by changes in the respiratory mechanics. The regulation of this pattern is qualitatively consistent with hypotheses based upon optimization criteria and involves alteration of both the respiratory frequency (f) and tidal volume (V_T) as their product of minute ventilation ( ) varies. The particular f-V_T relationship followed both in theory and observed response is influenced by changes in respiratory mechanics produced by loading. Within the breath, volume and durations of inspiration and expiration also respond to applied loads. The inspiratory terminating threshold curve is shifted to the left by elastic (E) loading and to the right by flow resistive (R) loading. Regulation of the end-expiratory volume (EEV) is provided by regulation of laryngeal resistance, control of inspiratory muscle tone during expiration, and activation of expiratory muscles. Separation of the contributions of humoral, subconscious neural, and perceptual reflexes responding to loading is important to enable assessment of the effects of sleep or pathology upon specific aspects of pattern regulation. A loading technique is described that permits the reliable estimation of breathing pattern responses to mechanical loads below the threshold for conscious perception, producing immediate response estimates attributable only to neural reflexes and intrinsic muscle characteristics.     

On the depth of the cyclopean retina

Summary The maximum disparity which can elicit depth perception was measured in dynamic randomdot stereograms as a function of stimulus size and duration. Maximum disparity increased with size as a function of the square root of stimulus area, and depth could under optimal conditions be perceived up to several arc degrees of disparity, even for short (48 ms) durations of exposure. These data delineate the limiting disparity/depth characteristics of the cyclopean retina, and provide fresh evidence of the distinction between local and global disparity processing.C.W. Tyler was supported by NIH grants No. EY 02124, RR 0566 and the Smith-Kettlewell Eye Research Foundation     

Sigh rate and respiratory variability during normal breathing and the role of negative affectivity

Spontaneous breathing was measured in healthy persons scoring either high (N = 45) or low (N = 30) on trait negative affectivity (NA), during a 10 min period of quiet sitting using the LifeShirt System®. Sighing and respiratory variability before and after sighs were assessed. Total respiratory variability of minute ventilation was indexed by the coefficient of variation and structured (correlated) variability was quantified by the autocorrelation. Total variability was higher before a sigh than before a non-sigh, without concomitant differences in structured variability, suggesting more random variability before a sigh. After a sigh, correlated variability increased whereas it remained the same after a non-sigh. Thus sighing acted as a resetter of the respiratory system. However, when comparing the low and the high NA group, this pattern was specific for high NA individuals. We conclude that it is important to take into account individual difference variables when studying the psychophysiological functions of sighing.