beta-Endorphin modulation of pressor response to hyperventilation in hypertensive patients

Plasma nociceptin/orphanin FQ levels in response to the hyperventilation test in healthy subjects

In vitro and in vivo studies demonstrated that nociceptin/orphanin FQ inhibits norepinephrine release, while the effects of norepinephrine on nociceptin/orphanin FQ release remain unknown. Previous studies in healthy and hypertensive subjects showed that prolonged and forced hyperventilation induces different blood pressure (BP) responses depending on changes in plasma catecholamine levels. We investigated whether the effects of hyperventilation on the sympatho-adrenergic system involve nociceptin/orphanin FQ release. Fifty-six healthy subjects (26 females, mean age 63+/-2 and 30 males, mean age 63+/-3) underwent the hyperventilation test. A hierarchical cluster analysis based on BP response to hyperventilation identified three groups of subjects: group 1 (n=20) with a decrease in BP, norepinephrine (1311.1+/-45.5 fmol/ml versus 900.0+/-55.3 fmol/ml, P<0.01) and nociceptin/orphanin FQ (13.0+/-0.7 pg/ml versus 7.9+/-0.8 pg/ml, P<0.01), group 2 (n=18) without any change in BP and norepinephrine (1133.0+/-31.5 fmol/ml versus 1176.0+/-44.6 fmol/ml), with a decrease in nociceptin/orphanin FQ (12.5+/-3.2 pg/ml versus 7.4+/-0.6 pg/ml, P<0.01) and group 3 (n=18) with an increase in BP, norepinephrine (1216.7+/-50.9 fmol/ml versus 1666.7+/-44.9 fmol/ml, P<0.01) and nociceptin/orphanin FQ values (11.5+/-1.6 pg/ml versus 19.9+/-1.5 pg/ml, P<0.01). Norepinephrine changes in response to hyperventilation in groups 1 and 3 were directly (P<0.01) correlated with those of nociceptin/orphanin FQ. Our results showed that vigorous and prolonged hyperventilation changes plasma nociceptin/orphanin FQ levels due to the direct effects of hypocapnic alkalosis or to different sympatho-adrenergic system responses.

Pressor responses to hyperventilation in elderly subjects differentiate essential from secondary hypertension

We evaluated pressor responses to the hyperventilation test in elderly normotensive (n=43, mean age 82 ± 5 years) and elderly hypertensive subjects (n=45 with essential hypertension, mean age 82 ± 2 years, and n=49 with secondary hypertension, mean age 82 ± 3 years). Hyperventilation did not change blood pressure (BP) in normotensive and secondary hypertensive subjects, whereas it decreased BP in essential hypertensives. Hierarchical cluster analysis based on BP responses to hyperventilation disclosed three groups of subjects in each population: group 1 exhibited a reduction in BP (essential hypertensives: 76%), group 2 no change (normotensives: 70%, secondary hypertensives: 76%), and group 3 an increase (normotensives: 19%, essential hypertensives: 13%, secondary hypertensives: 14%). Ambulatory BP monitoring found significant differences in pressor daytime profiles of hypertensive patients according to pressor responses to hyperventilation showing wide fluctuations in group 1 and 3 patients. Interestingly, the peak ambulatory SBP values correlated to the pre-hyperventilation SBP values in group 1, and to the hyperventilation peak SBP values in group 3. In conclusion: 1) Aging decreases reactivity to respiratory alkalosis in elderly normotensives; 2) hyperventilation induces significant pressor changes frequently in essential hypertension, but rarely in secondary hypertension; 3) the significant pressor responses to hyperventilation reflect the daytime pressor profiles predicting the highest daily fluctuations of BP values.

The validity of a hyperventilation test for an investigation of autonomic failure: assessment in patients with multiple system atrophy and Parkinson's disease

Although heart rate (HR) responses to hyperventilation (HV) have been used as a cardiovascular autonomic function test, autonomic involvement during HV remains uncertain. To clarify the relationship between autonomic activity and cardiovascular changes during HV, we compared cardiovascular responses during HV among subjects with different autonomic function, namely 16 patients with probable multiple system atrophy (MSA), 16 with possible MSA, 28 with Parkinson's disease (PD) and 28 healthy controls. Abnormalities of cardiovascular responses to head-up postural change and the Valsalva maneuver were definitely present in the order of probable MSA, possible MSA and PD, and abnormal HR and blood pressure (BP) responses during HV were observed in probable MSA and possible MSA, but not in PD. Unlike the significant difference in standard cardiovascular autonomic function tests, the HR and BP responses during HV were equivalent between probable and possible MSA. These findings suggest that cardiovascular control during HV may be affected not only by autonomic activity but also by other factors.

Blood pressure response to hyperventilation test reflects daytime pressor profile

Recent studies show that healthy subjects and patients with moderate hypertension have different pressor responses to hyperventilation, depending on their sympathoadrenergic reactivity. In the present study, we investigated whether a different response to the hyperventilation test is related to differences in the daily blood pressure profiles recorded with noninvasive ambulatory monitoring. Forty-five healthy subjects and 67 patients with essential hypertension of grades 1 and 2 (Joint National Committee VI and World Health Organization) were investigated. Healthy subjects and hypertensive patients responding to hyperventilation with an increase in systolic blood pressure had, during daytime ambulatory blood pressure assessment, peak systolic blood pressure values (146.0+/-5.0 mm Hg, 182.2+/-9.0 mm Hg, respectively) similar to the hyperventilation peak systolic blood pressure values (147.2+/-3.5 mm Hg, 183.0+/-4.7 mm Hg, respectively). Hypertensive patients responding to hyperventilation with a decrease in blood pressure showed clinic systolic blood pressure values (178.4+/-3.2 mm Hg) higher than daytime average ambulatory systolic blood pressure (155.2+/-7.1 mm Hg; P<0.01). Our results indicate that a hyperventilation test yields information on daily peak blood pressure values in healthy subjects and hypertensive patients when it induces a pressor increase and can identify hypertensive patients with the so-called "white coat effect" when it induces a pressor decrease.