The influence of cardiopulmonary receptors on long-term blood pressure control and plasma renin activity in conscious dogs

The isolated and combined influence of cardiopulmonary and arterial baroreceptor denervation on long-term blood pressure (MAP), heart rate (HR), plasma volume (PV) and plasma renin activity (PRA) was studied in 10 conscious, chronically instrumented foxhounds receiving a normal sodium diet. Cardiopulmonary denervation was achieved by surgically stripping both thoracic vagi. Near complete arterial baroreceptor denervation, leaving most cardiopulmonary fibres intact, was made by left vagal deafferentiation which has been shown to eliminate most aortic baroreceptor afferents, and a carotid sinus denervation. Five groups were studied: (I) control (n = 9), (II) cardiopulmonary denervation (n = 5), (III) aortic baroreceptor denervation (n = 5), (IV) arterial baroreceptor denervation (n = 4) and (V) total denervation (n = 6). No changes in PV were observed. Only group V revealed significantly higher levels of MAP (119.5 +/- 5.4 vs. 100.1 +/- 1.6 mmHg; P less than 0.05), HR (118.1 +/- 4.4 vs. 87.8 +/- 3.7 beats min-1; P less than 0.001) and PRA (3.0 +/- 0.8 vs. 0.9 +/- 0.2 ng AI m-1 h-1; P less than 0.05). It is suggested that the isolated function of either cardiopulmonary or arterial baroreceptors is sufficient to maintain these variables at a normal level. Contrary to the results of other reports the cardiopulmonary receptors do not seem to regulate MAP at a level about which the arterial baroreceptors operate. When both groups of afferents were interrupted MAP, HR and PRA rose to significantly higher levels, implying that cardiopulmonary and arterial baroreceptor afferents interact in a sense of a non-additive attenuation.     

Blood pressure and cardiac changes during signalled and unsignalled avoidance in dogs

Alterations in blood pressure (BP) during two aversive behavioral tasks were studied in five chronically-prepared dogs. During a signalled-avoidance task, BP levels were not altered, although heart rate (HR) increased. While propranolol (0.3 mg/kg, IA) led to slight increases in resting pressure, and phenoxybenzamine (1.0 mg/kg) reductions, the tachycardia at avoidance onset was not affected. Exposure to an unsignalled-avoidance task led to elevated diastolic BP levels during a preavoidance period and to increases in systolic BP, HR and aortic dP/dt at the inception of the avoidance session. Again, neither drug affected the tachycardia during avoidance, but both agents precluded BP and aortic dP/dt increases. Patterns of intercorrelations among cardiovascular variables were similar for both tasks, and suggested that the basis of the BP maintenance shifted from vasomotor to cardiac control during the avoidance periods. The differential cardiovascular adjustments during these tasks could not be accounted for in terms of differences in response rate. Rather, the critical variable seemed to be the amount of feedback the animal received for responding.     

Renal sodium handling in intact and renal denervated dogs

The ability to retain sodium was investigated in six conscious dogs before and after surgical renal denervation. Dietary sodium and water intake were kept constant (2.5 mmol Na X kg-1 bw X day-1 and 91 ml water X kg-1 bw X day-1). Balance experiments were performed from 6 days before to 8 days after having produced a sodium deficit of 6.4 +/- 0.4 (intact dogs) and 5.8 +/- 0.2 (renal denervated dogs) mmol Na X kg-1 bw by means of a peritoneal dialysis (PD). Having the same sodium excretion before PD, intact and renal denervated dogs demonstrated a similar striking decrease of sodium excretion and a similar increase of plasma renin activity after PD until the amount of sodium lost had been replenished (4th day after PD). In intact and renal denervated dogs plasma sodium concentration (PNa) decreased and renal water excretion increased on the first day after PD, indicating a homeostatic response to the fall of PNa. After dietary sodium restriction (from 2.5 to 0.5 mmol Na X kg-1 bw X day-1) a similar striking decrease of renal sodium excretion occurred in intact and renal denervated dogs. It therefore is concluded that in conscious dogs the presence of the renal nerves is not essential in order to maintain body sodium homeostasis after an acute sodium loss or after dietary sodium restriction.     

Long-term experimental electric stimulation of denervated laryngeal muscles in dogs. Myopathologic findings

The recurrent laryngeal nerve was transsected unilaterally and a device for electrical stimulation of the denervated muscles was implanted in 6 dogs. After 3 to 11 months the laryngeal muscles were obtained and histopathologically demonstrated a striking neurogenic pattern. In place of homogeneous muscle fiber atrophy, a patchwork of grouped fibre atrophy, compensational hypertrophy, fibre regeneration and reinnervation as well as muscle fibre type grouping were observed. Muscle fibre type distribution in the m. cricoarytenoideus posterior, m. vocalis and m. cricothyroideus was determined and compared between the normal and denervated sites. All muscles showed some changes in the fibre type distribution, including type grouping, but these were most pronounced in m. vocalis. The average fibre diameter decreased whereas fibre size variability increased. Mixed muscle fibre atrophy with compensatory hypertrophy of a single fibre type predominated. There was no evidence of disuse atrophy. The electrically stimulated muscles could be maintained at a reduced functional level throughout the study period.     

Blood pressure control in treated hypertensive patients: clinical performance of general practitioners.

BACKGROUND: The blood pressure of many treated hypertensive patients remains above recommended target levels. This discrepancy may be related to general practitioners' (GPs') actions. AIM: To assess clinical performance of GPs in blood pressure control in treated hypertensive patients and to explore the influence of patient and GP characteristics on clinical performance. DESIGN OF STUDY: Cross-sectional study conducted on 195 GPs with invitations to participate made via bulletins and by letter. SETTING: One hundred and thirty-two practices in the southern half of The Netherlands from November 1996 to April 1997. METHOD: Performance criteria were selected from Dutch national hypertension guidelines for general practice. GPs completed self-report forms immediately after follow-up visits of hypertensive patients treated with antihypertensive medication. RESULTS: The GPs recorded 3526 follow-up visits. In 63% of these consultations the diastolic blood pressure (DBP) was 90 mmHg or above. The median performance rates of the GPs were less than 51% for most of the recommended actions, even at a DBP of > or = 100 mmHg. Performance of non-pharmacological actions increased gradually with increasing DBP; prescribing an increase in antihypertensive medication and making a follow-up appointment scheduled within six weeks rose steeply at a DBP of > or = 100 mmHg. Patient and GP characteristics contributed little to clinical performance. Action performance rates varied considerably between GPs. CONCLUSION: GPs seem to target their actions at a DBP of below 100 mmHg, whereas guidelines recommend targeting at a DBP of below 90 mmHg.     

Interplay among carotid sinus, cardiopulmonary, and carotid body reflexes in dogs.

Interactions among vascular reflexes evoked from carotid sinuses, carotid bodies, and cardiopulmonary region were examined in anesthetized, atropinized, and respired dogs with aortic nerves cut. The carotid sinuses were perfused at 220, 150, and 40-50 mmHg; the chemoreceptors were stimulated by perfusion with hypoxic hypercapnic blood. Cardiopulmonary vasomotor inhibition was interrupted by vagal cold block. Measurements were made of arterial blood pressure and of kidney and hindlimb vascular resistance. At sinus pressures less than 170-160 mmHg, cardiopulmonary vasomotor inhibition increased with increase in blood volume. At high sinus pressure, interruption of this augmented cardiopulmonary inhibition was as ineffective in changing vascular resistance as interruption of the lesser inhibition present during normovolemia. Chemoreceptor stimulation increased the response to vagal block at intermediate but not at high or low sinus pressure. The studies demonstrate the dominant role of the carotid sinus reflex when the three systems interact and the ineffectiveness of chemoreceptor stimulation when carotid or cardiopulmonary inhibition is maximal.     

Effect of exercise on fractional extraction of catecholamines by the denervated heart in conscious dogs.

To examine the applicability of Halter's assumption to the denervated heart during exercise, we measured the concentrations of norepinephrine (NE) and epinephrine (E) in arterial and coronary sinus plasma in cardiac denervated dogs. As the level of exercise was increased from 0 (at rest) to 3, 6, and 12 km/h, fractional extraction (FE) of NE significantly decreased from 51 +/- 7 to 39 +/- 5, 34 +/- 6, and 30 +/- 5%, respectively. FE of E did not decrease at exercise (at rest, 57 +/- 10; 3 km/h, 60 +/- 9; 6 km/h, 60 +/- 5; and 12 km/h, 66 +/- 6%). There was no significant difference between FE of NE and E at rest and at 3 km/h, but FE of NE was significantly less than that of E with 6 and 12 km/h exercise. We conclude that FE of NE by the denervated heart decreases during exercise, and that FE of NE and E are approximately equal at rest and at mild exercise, but not at strenuous exercise.     

Blood pressure fluctuations in human nailfold capillaries.

Dynamic blood pressure was measured in 33 human finger nailfold capillaries after direct cannulation with glass micropipettes by means of a resistance servo-nulling pressure measuring method. ECG, finger pulsations, and respiratory thorax excursions were monitored simultaneously. All recordings exhibited pulsatile oscillations related to the cardiac rhythm. These oscillations resembled the wave forms of arterial pulsations with steep upstroke and dicrotic notch when the pressure amplitudes were above 10 mmHg. There was no apparent dependence on respiration. In 12 instances, pressure fluctuations with frequencies ranging from 0.2 down to 0.07 Hz were observed in both the arteriolar and venular limb. Blood pressure in human skin capillaries is pulsatile and subject to remarkable fluctuations in the arteriolar as well as in the venular limb, systolic pressure values ranging from 14 to 71 mmHg and from 11 to 52 mmHg, respectively.     

Blood pressure and self-concept among African-American adolescents.

Differences in blood pressure among individuals of African ancestry living in the United States compared with those living in Africa suggest that the high prevalence of hypertension among African Americans may be due in part to environmental factors. There are a number of environmental models that attempt to account for the high rate of hypertension among African Americans. One model proposes that a strong African self-concept protects African-American adolescents from the hypertensive effects of social stress. This model was tested during a blood pressure survey of 333 adolescents in three urban Los Angeles high schools. African self-concept was assessed using a three-item scale. The average score for the three items was strongly related to systolic blood pressure among African-American male adolescents. After controlling for age, body mass index, and parent''s education in regression analyses, the relation was reduced, but an effect remained. The model suggests that the hypertensive effects of the environment will operate unless the pathway from environmental stress to hypertension is blocked by a strong African-American self-concept.     

Antibodies to the acetylcholine receptor in myasthenic dogs.

Antibodies to the AChR and anti-striational antibodies have been detected in dogs suffering from myasthenia gravis. The detection of these antibodies adds to the known similarities between the human and canine disease. This animal model will facilitate investigation of agents involved in the induction of spontaneous myasthenia gravis.