Instantaneous Respiratory Rate Research Articles

Estimation of Breathing Rate from Respiratory Sinus Arrhythmia: Comparison of Various Methods

Although respiratory sinus arrhythmia (RSA) is a well-known and often studied phenomenon, methods to estimate (average) respiratory rate from heart rate variability via RSA have been investigated and published only sparsely. We reinvestigate three published techniques and contrast them to our own approaches. All methods were also evaluated for respiration signals to yield approximations of the true breathing rate for comparison. Our analyses are based on physiological recordings available at PhysioNet, an online database. Results show that the RSA of young supine subjects yields good approximations of mean respiratory rate in the case of time series longer than 1 min, while the estimations become noticeably less accurate for elderly persons. Our own "advanced counting method" produced the best results, and in addition principally permits even the definition of instantaneous respiratory rates. Consequently, it is recommended for further investigations.

Development of respiratory rhythms in perinatal chick embryos

In chick embryos, gas exchange takes place via the chorioallantoic membrane (CAM) and the lungs at approximately 1 day prior to hatching. The present study was designed to elucidate the development of respiratory rhythms in the chick embryo during the whole pipping (perinatal) period with a condenser-microphone measuring system. The microphone was hermetically attached on the eggshell over the air cell on day 18 of incubation. It first detected a cardiogenic signal (i.e. acoustocardiogram), and then beak clapping and breathing signals (acoustorespirogram, ARG). The first signals of lung ventilation appeared intermittently and irregularly approximately once per 5 s among the clapping signals after the embryo penetrated its beak into the air cell (internal pipping, IP). The respiratory rhythm then developed irregularly, with a subsequent more regular rate. The envelope pattern of breathing from the onset of IP through external pipping (EP) to hatching was constructed by a specially devised procedure, which eliminated external and internal noises. The envelope patterns indicated that the IP, EP and whole perinatal periods of 10 embryos were 14.1±6.4 (S.D.), 13.6±4.0 and 27.6±5.4 h, respectively. In addition, they also indicated the period of embryonic hatching activity (i.e. climax) which was 48±19 min. The development of respiratory rhythm was also shown by the instantaneous respiratory rate (IRR) which was designated as an inverse value of two adjacent ARG waves.

Effects of hypoxia and hypercapnia on patterns of sleep-associated apnea in elephant seal pups.

This project examined the effects of alterations in respiratory drive on the occurrence of sleep apnea in Northern elephant seal pups (Mirounga angustirostris). Sleep pattern was unaffected by levels of hypoxia (approximately 13%) or hypercapnia (approximately 6%) that doubled respiratory frequency during slow-wave sleep (SWS). During sleep in air, short periods of continuous breathing (mean length = approximately 2.6 min) alternated with periods of apnea (mean length = approximately 6.1 min). Under hypoxic or hypercapnic conditions, the frequency of occurrence of apneas was reduced primarily due to the occurrence of some sleep episodes without periods of apnea. In episodes in which apneas did occur, they began later in the sleep episodes, but their length and the length of the periods of eupnea were not significantly altered. During each period of eupnea, however, the instantaneous respiratory rate and the total number of breaths increased. Breathing during sleep was restricted to SWS, never occurring during rapid eye movement (REM) sleep, regardless of the respired gas mixture. If the levels of hypoxia and hypercapnia were raised further, all episodes of apnea during sleep could be eliminated together with all episodes of REM sleep. One interpretation of the data is that the threshold for altering breathing during eupnea (instantaneous breathing frequency and number of breaths per episode of eupnea) is lower than that for altering the lengths of the periods of apnea and eupnea and that the muscle atonia associated with REM sleep extends to all respiratory muscles.

Effect of continuous positive airway pressure breathing on cardiorespiratory function in infants with respiratory distress syndrome.

A method of investigating the cardiorespiratory responses to continuous positive airway presslre (CPAP) in infants with respiratory distress syndrome is described. All measurements were made immediately before and within five minutes of application or any change in level of CPAP. Ventilation was derived from a pneumotachograph and dynamic compliance calculated. We have also measured arterial pH, oxygen and carbon dioxide tensions, arterial blood pressure and central venous pressure. Arterial oxygen tension increased in association with a decrease in the alveolar-arterial oxygen gradient. No consistent changes occurred in pH or carbon dioxide tension. Heart rate and mean arterial blood pressure remained the same but the arterial pulse pressure narrowed and the increase in central venous pressure averaged 17% of the applied airway pressure. There were less variations in both tidal volumes and instantaneous respiratory rates with CPAP compared with spontaneous breathing without CPAP. The respiratory rate decreased, but there were no consistent changes in tidal volume, resulting in a lesser reduction of minute ventilation. Dynamic compliance decreased on CPAP. With correct use of CPAP, and improvement in oxygenation generally occurs without obvious adverse cardiorespiratory effects. CPAP must nevertheless be used cautiously and in conjunction with close monitoring; because when the appropriate pressures are exceeded, it is possible that both circulatory and ventilatory function might be severely compromised.