CHANGES IN HEART-RATE DURING OBSTRUCTIVE SLEEP-APNEA

The mechanisms behind the decrease in heart rate during apnoeas in patients with obstructive sleep apnoea (OSA) are little known. Recent findings in animal experiments indicate that stimulation of the upper airway activates postinspiratory and cardiac vagal neurones in the medullary respiratory centre, causing alterations in heart rate and respiratory rhythm. Since OSA leads to a collapse of the airway and consequent stimulation of upper airway receptors, we studied the interrelations between heart rate and respiratory rhythm during apnoea and during negative intrathoracic pressure generated by the Mueller manoeuvre (MM). Fifteen patients with OSA (apnoea hypopnoea index (AHI) 45+/-28.h-1) were studied by polysomnography, during a MM and a Valsalva manoeuvre, each of 15 s duration. The heart rate decrease (DELTA-HRA) and the increase in total respiratory cycle duration (TOT) were evaluated during apnoea in non-rapid eye movement (REM) sleep. Patients with OSA demonstrated a decrease in heart rate during apnoea (-14.4+/-beats.min-1), and during MM (-11.5+/-13.5 in OSA vs 3.1+/-7.8 beats.min-1 in a control group). TOT increased during apnoea (4.6+/-3.1 s). There was a significant correlation between DELTA-HRA and AHI (r=-0.64) as well as between DELTA-HRA and increase in TOT(r=0.62). These findings indicate that upper airway obstruction may cause an activation of receptors at the site of airway collapse or distortion leading to changes in heart rate and respiratory rhythm.