The relationship between cardiac output and posthyperventilation hyperpnoea in patients with essential hypertension

Abstract

aaFollowing abrupt cessation of voluntary hyperventilation, ventilation declines gradually towards the baseline. This phenomenon has been called posthyperventilation hyperpnoea (PHVH), and it is believed to be due to the activation of a reverberating circuit of neurons in the respiratory centre area [1]. This reverberating circuit is activated along with the respiratory neurons and provides sufficient input to the respiratory centres to maintain ventilation after the decrease in chemoreceptor activity [1]. It has been demonstrated that different factors, such as the changes in arterial pH and CO 2 tension [2,3], blood progesterone levels [4], and respiratory frequency during hyperventilation [3], can affect the duration of PHVH.It is well known that increases in cardiac output (CO) are followed by an increase in respiratory frequency and minute ventilation (V'E) in dogs [5,6]. However, there is evidence that during voluntary hyperventilation CO is substantially raised in healthy subjects [7,8]. Thus, it has been suggested that the increase in CO occurring during voluntary hyperventilation may affect the duration of PHVH [2]. It is also known that, in hypertensive patients, the increase of CO in response to exercise is less pronounced [9]. Therefore, if PHVH is influenced by the rise in CO during voluntary hyperventilation, hypertensive patients are expected to have a shorter duration of PHVH, thus providing a model to study the determinants of the PHVH phenomenon in humans. To test this hypothesis, the duration of PHVH and the changes in CO during voluntary hyperventilation in patients with essential hypertension and in healthy subjects were assessed. Materials and methodsWe studied 20 male patients with essential hypertension (age range: 29-62 yrs) and 12 age-matched male healthy subjects (controls). Four hypertensives and two controls were current smokers. The mean values (±SEM) of arterial blood pressure were 178/107±3/1 and 121/71±2/2 mmHg in hypertensives and controls, respectively. Hypertensive patients belonged to stage I or II of the World Health Organization (WHO) classification and showed no concurrent illness, including respiratory tract disorders. Antihypertensive drugs were withdrawn Š4 weeks before the study. Subjects were not allowed to drink beverages containing xanthines for Š24 h before the study. The study was approved by the Ethics Committee of the University of Catania, and each subject gave informed consent to participation in the study.Subjects were seated and breathing through a face mask to which was attached a turbine flow head to measure airflow. A sampling line for the collection of end-expiratory gases was also connected to the face mask. After 10 min of quiet breathing, subjects were asked to perform sustained This hypothesis was tested by measuring the duration of PHVH in patients with essential hypertension, in whom the increase in CO as a result of various stimuli is less pronounced. Twenty male hypertensives (mean arterial blood pressure±SEM: 178/ 107±3/1 mmHg), and 12 age-match...