Heart Rate Variability during Respiratory Pauses in Puppies and Dogs

Abstract

De [~ur~mrrztt c~/'Pm/rutrrc~.c (Pulrnonury Dirr.cion) I tot, total respiratory max(RR), maximum R R interval within a respiratory cycle min(RR), minimum R R interval within a respiratory cycle range(RR), difference between min(RR) and max(RR) NTS, nucleus tractus solitarius N A , nucleus ambiguus V M N , vagal motoneuronsnumber of years (3). We have demonstrated previously that HRV is abnormal in certain groups of infants who are at risk of sudden death (4, 5) and more recently, it as been shown that HRV can be used to estimate cardiac age in adult humans (ti. 7).We (8) and others (9-12) have previously examined the relation between breathing and heart rate and found that HRV is closely tied to breathing in mature subjects. However, HRV is not determined only by breathing, especially in early life (8. 12). For instance, during apnea or lack of breathing, heart rate varies, albeit much less than during breathing. These heart rate changes during respiratory pauses have not been studied in detail. For example, we d o not know the time course of the change in RR interval during pauses in early life and how these changes compare with those in the mature subject. In order to understand further the mechanisms that control heart rate and HRV, we examined herein the time course and the change in heart rate during respiratory pauses and compared them to those during breathing. Since the ANS is not mature early in life (8,(12)(13)(14) and since the ANS plays a major role in HRV (10). we studied the heart rate response to a respiratory pause in early life (puppies) and in an adult mature animal (dog). METHODS

Thermoregulatory Control of Feeding and Sleep in Premature Infants

“…It should also be noted that the feeding episode occurs after an episode of active sleep (and awakening), a sleep stage during which sympathetic outflow is dominant (13). Several authors (14, 15, 16) have shown that physiological events occurring in an active sleep episode just before awakening are characterized by an increase of activation level (increase of body motility and respiratory and cardiac frequencies). Unfortunately, these authors have never related these events to a possible sympathetic outflow that could be integrated to a thermoregulatory food intake episode.…”

Heart rate variability

“…* Many neurological and psychological investigations have used HRV to evaluate the effects of stress, emotion, and work on the autonomic nervous s y~t e r n ,~-l~ including very specialized investigations. l 4 Quantification of HRV has also been used as the standard for evaluating other psychological methods. I 5 Physiological studies in humans have reported an increase of HRV, interpreted as an increase of cardiac va- gal tone at rest, following intensive exercise for several days.…”

Episodic bradycardia in preterm infants.

“…Bradycardia often starts during the early stages of apnoea, however, and most authors now consider that a reflex response is more likely.2 6 7 Our group originally postulated that reflex bradycardia was most commonly related to respiratory effort against a closed glottis during upper airway obstruction.7 This view has been challenged by Henderson-Smart et al, who suggested a peripheral chemoreceptor response to falling oxygen saturation (Sao2) was the most likely explanation.8 Experiments on immature animals, however, have shown that heart rate changes occur at the beginning of respiratory pauses before any change in arterial blood gases. 9 Oxygenation would appear to exert an important influence, though. We have recently reported that initial Sao2 before the onset of apnoea is significantly lower in those episodes which result in bradycardia.…”