Biomedical subjects

A U Ferrari

Publications and source records attributed to A U Ferrari.

42 records · Page 3Linked to original sources

PubMed1988

Evaluation of baroreceptor reflex by blood pressure monitoring in unanesthetized cats.

The arterial baroreceptor control of the sinus node operating in unanesthetized conditions was evaluated in 10 cats in which blood pressure was recorded intra-arterially and scanned by a computer to identify the "spontaneous" sequences of three or more consecutive beats in which systolic blood pressure (SBP) progressively rose and pulse interval (PI) progressively lengthened (type 1 sequences) or SBP progressively fell and PI progressively shortened (type 2 sequences). Many type 1 and 2 three-beat sequences were found; four-, five-, and six-beat sequences of either type were progressively less common, and sequences longer than six beats were almost never identified. The regression coefficient was 30% greater for type 1 than for type 2 sequences. However a prominent feature of either regression coefficient was a wide scattering in each cat (average variation coefficient 50.9 +/- 5.5%). The regression coefficient values were related to some extent to the PI but not to the SBP existing at the beginning of the sequence. Sinoaortic denervation dramatically reduced the number of sequences of either type. These data validate a method for collecting a large number of observations on the baroreceptor-heart rate reflex in physiological conditions. This method may improve understanding of baroreflex involvement in integrated cardiovascular regulation.

Animals↗

PubMed1987

Effects of altering the interval between the stimulus and the reflex response in the analysis of the baroreceptor control of the sinus and atrioventricular nodes in man.

Baroreceptor control of the sinus node may be determined by raising or lowering blood pressure with intravenous bolus injections of phenylephrine or glyceryl trinitrate and calculating the slope of the linear regression between the drug induced changes in systolic blood pressure and RR interval using shift 1 coupling--namely, coupling of each systolic blood pressure value with the interval of the following cardiac cycle. To assess whether shift 1 coupling provides the best linear fit and the highest regression slope nine subjects received phenylephrine and glyceryl trinitrate injections both during spontaneous sinus rhythm and during atrial pacing to evaluate baroreflex control of the sinus and of the atrioventricular node respectively. In regression analysis of the data, for each drug injection nine different shifts (from 0 to 8) were used to couple systolic blood pressure with RR or StQ intervals. When the mean results from all subjects were compared the use of shift 1 was equal or superior to the use of any other shift for both the RR and the StQ interval responses evoked by either phenylephrine or glyceryl trinitrate. In many instances, however, the shift that provided the highest correlation and regression coefficient was different from shift 1, and the use of these best individual shifts provided results considerably different from those obtained with the standard shift 1. It is concluded that in the regression analysis of baroreflex cardiac responses to vasoactive drugs the regular use of shift 1 does not invariably provide the best estimation of baroreflex sensitivity. This is better achieved by calculating the best shift in individual responses.

Atrioventricular Node↗

PubMed1987

Sensitization of aortic baroreceptors by high salt diet in Dahl salt-resistant rats.

High salt diet alters neural cardiovascular control. This influence has been attributed to central neural or efferent mechanisms. To test the hypothesis that a high salt diet might alter afferent baroreceptor function, Dahl salt-resistant (DR) and salt-sensitive rats (DS) were fed a high or a low salt diet. Blood pressure was measured intra-arterially in unanesthetized animals. Aortic baroreceptor function was then evaluated during urethane anesthesia by recording multifiber aortic depressor nerve activity during a phenylephrine-induced blood pressure ramp. Mean arterial pressure in the conscious state was elevated (155 +/- 5 [SE]mm Hg) in DS fed a high salt diet but was normal in DS fed a low salt diet and in DR. Slopes of linear regressions relating aortic nerve discharge to mean arterial pressure were 71% higher in DR fed a high salt diet than in DR fed a low salt diet (p less than 0.025), indicating that high salt potentiated baroreceptor function in DR. In contrast, high salt diet produced no significant effects on baroreceptor function in DS. No salt-induced changes in dynamic or static aortic distensibility (assessed from pressure-volume curves of the in situ isolated arch) were detectable in either rat strain. Absence of salt-induced baroreceptor sensitization in DS was not due to the hypertensive state because the sensitization also failed to occur in separate groups of DS in which salt-induced hypertension had been prevented by chemical sympathectomy with 6-OH-dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Inverse relationship between heart rate and blood pressure variabilities in rats.

The interplay of heart rate variability, baroreceptor control of heart rate, and blood pressure (BP) variability was examined in chronically instrumented, unanesthetized, freely moving rats in which the efferent neural influences on heart rate were pharmacologically altered. In each rat, BP was recorded continuously for 90 minutes in the control condition and in one or more of the following conditions: 1) beta-adrenergic receptor blockade by propranolol, 1 mg/kg; 2) cholinergic blockade by atropine, 0.75 mg/kg, and 3) combined blockade by propranolol plus atropine. Each BP recording was analyzed beat-to-beat by a computer that calculated heart rate and BP variabilities, both expressed as variation coefficients. In addition, under each condition the sensitivity of the arterial baroreceptor control of heart rate was assessed by measuring the reflex changes in pulse interval in response to BP changes induced by bolus i.v. injections of phenylephrine and nitroprusside. As compared with the control condition, 1) propranolol (n = 10) reduced heart rate variability by 23 +/- 4% (p less than 0.01), only slightly impaired baroreceptor reflex sensitivity, and did not significantly modify BP variability (+11 +/- 7%); 2) atropine (n = 11) reduced heart rate variability by 30 +/- 7% (p less than 0.01), drastically impaired baroreceptor reflex sensitivity, and increased BP variability (+40 +/- 8%, p less than 0.01); 3) combined blockade (n = 10) caused variability and baroreceptor reflex changes similar to those induced by atropine alone. Thus, heart rate variability depends on both vagal and sympathetic influences. However, only the former component affects BP variability, that is, it plays an antioscillatory role.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

A new approach to analysis of the arterial baroreflex.

The arterial baroreflex is commonly evaluated by measuring the lengthening and shortening in pulse interval in response to changes in systolic (S) blood pressure (BP) induced by infusion of vasopressor and vasodepressor drugs. This method is simple but has important limitations: only a few observations can be made, reproducibility of the responses is far from optimal, interference by direct drug action on the sinus node and the baroreceptors cannot be excluded and the artificially induced stimuli only poorly mimic the naturally occurring pressor and depressor transients. A new approach was therefore pursued. Blood pressure was recorded intra-arterially for 3 +/- 0.4 h (mean +/- s.d) in 10 unanaesthetized, unrestrained cats and the recording was scanned by a computer to identify the spontaneous sequences of three or more consecutive beats in which SBP progressively rose and pulse interval progressively lengthened (type 1 sequence) or SBP progressively fell and pulse interval progressively shortened (type 2 sequences). Accurate beat-to-beat measurements of SBP and pulse interval were obtained by adopting a very narrow sampling interval of the BP trace, i.e. 1.6 ms real time. For each sequence the regression between the SBP values and the pulse internal values of the following cycle was calculated. In each cat a large number of three-beat sequences were found, the four-, five- and six-beat sequences being, however, progressively less common. All sequences had a high correlation coefficient (r > 0.9), type 1 having a greater slope than type 2 (14.1 +/- 2.5 versus 10.3 +/- 7.6 ms/mmHg, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Primary impairment of cardiopulmonary baroreflexes in Dahl salt-sensitive rats.

Neural mechanisms contribute to salt-induced hypertension in Dahl salt-sensitive (DS) rats. We examined whether cardiopulmonary (CP) baroreflexes are impaired in prehypertensive DS rats. Dahl salt-resistant (DR) and DS rats fed low salt diet were urethane-anaesthetized and sino-aortic denervated. Reductions in sympathetic activity (SNA, splanchnic nerve recording) were measured while CP baroreceptors were stimulated by volume expansion by dextran infusion (stimulus quantitated by changes in left ventricular end-diastolic pressure, LVEDP). Baseline arterial pressure, LVEDP and SNA were similar in the two groups. With dextran administered in equal amounts, LVEDP rose 25% more but SNA fell 20% less in DS than DR rats. Maximal CP baroreflex gain calculated as delta SNA/ delta LVEDP (in %/mmHg) was -3.6 +/- 0.4 in DS and -6.3 +/- 0.6 in DR rats (P less than 0.005). Heart weight and left atrial distensibility were similar in DR and DS rats. Thus DS rats with normal cardiac mechanical properties and blood pressure have impaired CP baroreflexes. This may contribute to salt-hypertension in these animals.

Animals↗