Maximum Pressure Change Research Articles

Environmental Determinants of Circadian Activity of Free-Ranging Iberian Lynxes

From February 1983 to May 1985, 12 Iberian lynxes ( Lynx pardinus ) (six adults and six juveniles) were radiotracked at hourly intervals for 114 24-h periods at Donana National Park, southwestern Spain. Nine environmental factors were related, by season and age class, to 12 indices of daily activity of lynxes derived from movement rates and pulses of the motion sensor in the transmitters. Coefficients of determination were higher in winter and summer than in spring. Juvenile lynxes appeared more sensitive to environmental factors than adults. Photoperiod had a major influence ( R 2 = 29%) on circadian activity pattern throughout the year. Environmental factors significantly related to activity of lynxes during winter were maximum temperature, pressure changes, evaporation, and moonphase. In summer, important variables were maximum temperature, moonphase, hours with moonlight, and high pressures. In spring, only rainfall and temperature (minimum and maximum) showed a slight but significant influence on activity of lynxes. Although some climatological factors may have a direct effect on the circadian activity of Iberian lynx, others (e.g., moonlight) may act indirectly by influencing the activity of the Mediterranean rabbit, the lynx's main prey.

Comparative effects on blood pressure and heart rate of dynorphin A(1–13) in anterior hypothalamic area, posterior hypothalamic area, nucleus tractus solitarius, and lateral cerebral ventricle in the rat

The objective of this study was to explore the effects of the endogenous opioid peptide dynorphin A(1–13) on the CNS regulation of blood pressure and heart rate. Wistar rats, anesthetized with pentobarbital and halothane, received dynorphin A(1–13) microinjected into the anterior hypothalamus area (AHA), the posterior hypothalamic area (PHA), the nucleus tractus solitarius (NTS), or the lateral cerebral ventricle (ICV). Dynorphin A(1–13), 20 (12 nmol) or 30 μg ICV, produced significant ( p < 0.05) reductions in blood pressure and heart rate. Naloxone, 50 μg/kg ICV, completely prevented the blood pressure response and significantly ( p < 0.05) blunted the heart rate response to the highest dynorphin concentration, 30 μg ICV (18 nmol). Dynorphin A(1–13), 5 μg, in the NTS significantly ( p < 0.05) decreased systolic and diastolic blood pressure and heart rate with the response being evident 10 min and persisting for 30 min after injection. In contrast, the same dose of dynorphin A(1–13) in the AHA produced an immediate, marked, and significant ( p < 0.05) decrease in systolic and diastolic blood pressure and heart rate that attained its maximum 1–3 min and returned rapidly towards baseline levels. Dynorphin A(1–13), 5 or 10 μg in the posterior hypothalamic area, was not associated with any change in blood pressure or heart rate. Injection of the diluent at any site was not associated with any changes in blood pressure or heart rate. The maximum change in blood pressure with dynorphin was greater in the AHA than NTS, and the maximum change in heart rate was greater in the NTS than AHA. These data indicate a potential role for dynorphin as a modulator of the CNS regulation of blood pressure and cardiac rate, and this is mediated in part through different areas in the brain that maybe localized to the anterior hypothalamic area and nucleus tractus solitarius but not the posterior hypothalamic area.

Splenectomy alters blood pressure response to incremental treadmill exercise in horses.

Six intact (IN) and five splenectomized (SP) mares were subjected to an incremental exercise test to examine the effects of splenectomy on blood pressure responses during exercise. During the test the horses ran up a 6 degree grade on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s every 1 min until heart rate (HR) reached a plateau. Hemodynamic data were collected continuously and analyzed for the last 18 s of the 4, 5, 6, and 7 m/s steps of the exercise test. There were no differences (P > 0.05) between the groups for resting means for any parameter measured in the study. HR increased (P < 0.05) in both groups of horses during exercise with significantly greater HR in the SP horses during the first two steps of the test. There were no differences (P > 0.05) in maximal HR between the groups. Right atrial pressure (RAP) did not change during exercise in the SP horses; however, it did increase 20 mmHg (493%, P < 0.05) in the IN horses. Right ventricular pressure (RVP) increased (P < 0.05) during exercise with no differences (P > 0.05) between the groups. Right ventricular maximum change in pressure over time increased (P < 0.05) in a similar fashion in both groups of animals. Mean arterial pressure (MAP) increased 29 mmHg (30%, P < 0.05) in SP horses, reaching a plateau by the 5 m/s step of the test.(ABSTRACT TRUNCATED AT 250 WORDS)

Early Assessment of Neurologic Deficits in the Fluid Percussion Model of Brain Injury

This study was designed to quantify the early neurologic effects of brain injury elicited by fluid percussion to the dura of cats. Propofol was used for surgical anesthesia because recovery in normal animals from an intravenous infusion was found to be nearly complete within 2 h of cessation and absolutely complete by 4 h. In addition, a cat coma scale (CCS) was developed that reflects normal (CCS, 14) to moribund (CCS, 3) behavior. The CCS values at 6 h were compared with the force of injury expressed in atmospheres (atm), maximum blood pressure change, and gross neuropathology to ascertain which parameter might best account for the behavior observed after brain injury. The results showed that decreasing neurologic scores correlated well with increasing atmospheres of injury (Pearson's r 0.71, p < 0.001) but not with the rise in systolic blood pressure caused by the trauma (n = 29). Coma scores did correlate with the cross sectional area of ponto-mesencephalic lesions (Pearson's r = 0.51, p < 0.01) and proved to be significantly different in animals grouped according to lesion size of less or more than 3 mm in length (t test, p < 0.01). Thus the CCS and the pharmacologic properties of propofol permit an early analysis of the neurologic status in the feline fluid percussion model of brain injury. These procedures could facilitate the evaluation of early biochemical changes that affect behavior and of therapies designed to ameliorate the deleterious effects of head injury.

The effects of propofol, methohexitone and isoflurane on the baroreceptor reflex in the cat.

The effects of propofol (P), methohexitone (M) and isoflurane (I) on the baroreceptor reflex were studied in a cat model in which the blood pressure in a bilateral isolated carotid sinus preparation was artificially varied between 50-200 mmHg. The influence from aortic and cardiopulmonary baroreceptors was excluded by vagotomy. With basal chloralose anaesthesia as control, the investigated anaesthetics were used in doses corresponding to MAC 0.5 and 1.0. The maximum change in systemic mean arterial pressure (MAP) and heart rate (HR) following a defined increase in carotid sinus pressure was used as an index of baroreceptor reflex sensitivity. Compared to control, M and I anaesthesia were associated with significant depression of baroreceptor reflex sensitivity at the high dose (corresponding to MAC 1.0), and during I anaesthesia also at the low dose (MAC 0.5). The baroreceptor reflex sensitivity was maintained during propofol anaesthesia. The carotid sinus pressure interval at which the maximum changes in MAP could be elicited, was significantly higher during M than during P. This indicates resetting of the baroreflex.

ETOMIDATE SHORTENS THE ONSET TIME OF NEUROMUSCULAR BLOCK

We have studied 30 healthy patients allocated randomly to receive thiopentone, propofol or etomidate in equipotent doses followed by vecuronium 0.1 mg kg-1. Haemodynamic variables and time to 100% neuromuscular block were measured. The patients receiving etomidate had a significantly shorter onset time of neuromuscular block compared with those receiving the two other i.v. induction agents. There was a significant negative correlation between onset time of neuromuscular block and the maximum percent change in mean arterial pressure.

Evaluation of techniques for delivery of steroids to lungs of neonates using a rabbit model.

Little is known about delivery of aerosolised steroids to neonatal patients undergoing assisted positive pressure ventilation and after extubation. A rabbit model has been established to investigate factors influencing drug delivery. Beclomethasone dipropionate, in a metered dose inhaler, was radiolabelled with technetium 99m. The mass median aerodynamic diameter of the aerosol was 3.3 (2.0) microns and the impactor measurements confirmed that the technetium distribution corresponded with that of the drug particles. The metered dose inhaler was actuated into a collapsible spacer that was used to ventilate and deliver aerosol to anaesthetised rabbits by a tracheostomy. From each actuation of the drug 2.9 (0.4)% of the aerosol deposited in the trachea and main bronchi and 1.2 (0.4)% in the lung. When the drug was delivered by a spacer device, with face-mask attachment, to rabbits breathing freely through a tracheostomy, aerosol deposition increased to 4.4 (2.1)% in the trachea and main bronchi and 1.9 (0.9)% in the lung lobes. The maximum change in systolic blood pressure after administration of aerosol by the collapsible spacer was a decrease of 13%. The methods described may prove useful for the delivery of inhaled steroids to neonatal patients likely to develop bronchopulmonary dysplasia.

Effect of secretin on lower esophageal sphincter pressure in patients with esophageal achalasia

The effect of a bolus intravenous administration of secretin (2.0 U/kg) on resting lower esophageal sphincter pressure (LESP) was investigated in seven patients with esophageal achalasia. Basal LESP before secretin injection in the patients was 60.1 +/- 3.4 mmHg (Mean +/- SEM), which was significantly higher than 26.9 +/- 2.5 mmHg in normal controls consisting of eight healthy volunteers. LESP significantly decreased within 1 min after the injection both in the patients and the controls. The maximum pressure change from each basal LESP was 31.2 +/- 5.2 mmHg in the patients, which was significantly greater than 12.1 +/- 1.8 mmHg in the controls. The effect of secretin disappeared within 5 min in the controls. The effect in the patients, however, lasted throughout the investigation time of 30 min. It is concluded that secretin has a long-acting effect on muscular relaxation of the lower esophageal sphincter in esophageal achalsia patients.

Induction of Changes in Internal Gas Pressure of Bulky Plant Organs by Temperature Gradients

Water manometers were connected to fruits of tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.), and then fruits were submerged in water baths providing initial temperature gradients between fruit and water of 0 to 19C. Apple (Malus domestics Borkh.) fruits, carrot (Daucus carota L.) roots, witloof chicory (Cichorium intybus L.) roots, rhubarb Rheum rhabarbarum L.) petioles, and pokeweed (Phytolacca americana L.) stems were subjected to water bath temperature gradients of 5C. Internal partial vacuums developed in all organs within minutes of imposing the gradients. The maximum partial vacuums in tomato and pepper fruits increased with increasing temperature gradients. Uptake of water accompanied changes in internal pressure reaching maxima of 17% (w/w) and 2% (w/w) of pepper and tomato fruits, respectively, after 22 hours. Maximum pressure changes achieved in bulky organs deviated from those predicted by the ideal gas law, possibly due to concomitant changes in gas pressure upon replacement of intercellular spaces with water and dissolution of CO2. Partial vacuums also developed in pepper fruits, rhubarb petioles, and pokeweed stems following exposure to air 15C cooler than initial organ temperatures. Results point to the role of temperature gradients in the transport of liquids and gases in plant organs.

Effects of an intravenously administered arrhythmogenic dose of bupivacaine at the nucleus tractus solitarius in the conscious rat.

This study was designed to further investigate the CNS-mediated cardiovascular toxicity of local anesthetics and to determine any effect of anesthesia on the firing rate of cells in the nucleus tractus solitarius (NTS) of conscious animals. Adult Sprague-Dawley rats were anesthetized with chloral hydrate. A femoral artery and vein were cannulated. A 3-mm hole was then drilled for placement of a unidirectional microdrive. The animal was removed from the stereotactic instrument, and EKG electrodes, pressure transducer and the microdrive containing a 1-micron tungsten electrode were attached. Animals were then placed in a canvas sling for recovery from the anesthetic. Cells of the NTS were located and cell firing rate (CFR) was continuously recorded. None of the animals exhibited any sign of discomfort upon recovery from anesthesia. CFRs decreased from 19 +/- 13 to 4 +/- 4 impulses/second at 20 +/- 16 seconds after the IV injection of bupivacaine (p less than 0.01). Maximum decreases in blood pressures were 26 +/- 15% of control and occurred at 32 +/- 14 seconds after the injection of bupivacaine. The maximum decrease in heart rate was 38 +/- 16% and occurred at 13 +/- 10 seconds after the injection of bupivacaine. Maximum heart rate changes occurred significantly earlier than maximum decreases in CFR (p less than 0.01). On the other hand, maximum blood pressure changes occurred significantly later than maximum decreases in CFR (p less than 0.01). The data reported here demonstrate that conscious animals respond similarly to animals anesthetized with chloral hydrate with respect to the medullary effect of local anesthetics.

Cardiovascular reactivity to the cold pressor test as a predictor of hypertension.

Cardiovascular reactivity to stress is hypothesized to be a marker for subsequent neurogenic cardiovascular disease, but few prospective studies of this hypothesis are available. We studied 910 white male medical students who had their blood pressure and pulse rate measured before and during a cold pressor test in the years 1948-1964. Hypertensive status (requiring drug treatment) was ascertained by annual questionnaires in the 20- to 36-year follow-up period. An association was observed between maximum change in systolic blood pressure and later hypertension, with a cumulative incidence of hypertension by age 44 of 6.7%, 3.0%, and 2.4% for a change in systolic blood pressure in the upper, middle two, and lowest quartiles, respectively (Kaplan-Meier, p less than 0.02). After adjustment for study entry age, Quetelet Index, cigarette smoking, pretest systolic blood pressure, and paternal or maternal history of hypertension in a Cox model, the association persisted. The excess risk associated with systolic blood pressure reactivity was not apparent until the population aged some 20 years and was most apparent among those in whom hypertension developed before age 45 (relative risk = 2.5, 95% confidence intervals = 1.47, 4.71 for a 20 mm Hg change). Diastolic blood pressure and heart rate changes were not associated with later hypertension. These data suggest that persons prone to later hypertension manifest an altered physiology at a young age.

Cardiovascular response to cerebral circulatory regulation during shifts in head position

Cardiovascular response and its effect on cerebral regulation was examined in groups of young and old people by putting pressure on the cerebral circulatory system through rapid changes in head position. A transient increase in blood pressure was observed in both the young and old people's groups when the head was tilted up. In the old group, there was less change in both systolic blood pressure and diastolic blood pressure. A transient reduction in blood pressure was observed in both groups when the head was tilted down. However, there was less change in diastolic blood pressure in the old group. The number of heart beats before a maximum change in blood pressure was 5 to 9 beats when the head was tilted up, and there was no significant difference between the two groups. The corresponding figure when the head was tilted down was 17.1 +/- 3.51 beats in the young group, and 27.1 +/- 11.5 beats in the old group, significantly higher among the old group. All were early responses observed within 1-2 minutes. Looking at the change of pulse after the head was tilted up or down among the young group, the number of heart beats increased to reach a peak when the head was tilted up, and when the head was tilted down the number of heart beats fell to its lowest level. The affect of these two cardiovascular responses tended to compensate for cerebral perfusion pressure, which indicates the possible existence of a cerebral perfusion pressure regulatory mechanism, assisted by a carotid sinus reflex. A reduction of this function was suggested in the old group.

The influence of eccentricity on the pressure distributions in O-ring seal contacts

In this work the influence of eccentricity on the pressure distributions of elastomeric seals of compact type are investigated. An O-ring seal with its simple section geometry is chosen as test object but the general trend of the results is expected to be valid for all elastomeric seals with homogeneous cross-sections. The theory used is based on the assumption that the seal contact element compression is the dominant contribution to the contact pressure. In order to couple contact element volume changes with pressure, the pressure-dependent seal material compressibility is used. The results show that the eccentricity does influence the contact pressure distribution if it is great enough. The most important parameter determining the maximum eccentricity is the parallel clearance gap. If this quantity is 0.3% of the unloaded seal cross-sectional diameter, the maximum pressure change is of the order 5%–10% when the eccentricity is changed from zero to its maximum value.

Influence of renal insufficiency on the pharmacokinetics and pharmacodynamics of terazosin

Renal insufficiency was not shown to affect the pharmacokinetics of terazosin in fifteen patients receiving oral terazosin (1 mg once daily) for two weeks. Five patients had normal renal function (creatinine clearance 80 ml per minute or more), five had moderate renal insufficiency (creatinine clearance 30 to 79 ml per minute), and five had severe renal insufficiency (creatinine clearance 10 to 29 ml per minute). Urine and blood samples were collected, and blood pressure and pulse rate were determined on days one and 15 of the study. Renal insufficiency had no significant effect on the absorption lag time, rate of absorption, rate of elimination in the urine, volume of distribution, or plasma clearance of terazosin. The plasma half-life of terazosin in patients with normal renal function was 10.0 hours, compared with 8.4 hours in patients with moderate renal insufficiency and 9.8 hours in the group with severe renal insufficiency. There was also no apparent relationship between renal insufficiency and the maximum change in blood pressure or pulse rate. Renal excretion was found to play a minor role in the elimination of terazosin, and this explains the lack of a relationship between renal insufficiency and the pharmacodynamics of terazosin. After the administration of terazosin on day 1 of the study, 1.6 ± 0.3 percent and 5.1 ± 1.4 percent of the total dose was excreted in the urine of patients with severe renal insufficiency and normal renal function, respectively. Adverse experiences were reported by four patients and caused one patient to withdraw from the study. Symptoms reported included gastralgia, headache, dizziness, malaise, weakness, and palpitations. The results of this study indicate that terazosin may be safely administered to patients with renal insufficiency without altering the usual dosing regimen.

Light stress and the cardiovascular system: the glare pressor test.

The effects of an impulsive glare of 4100 lx intensity upon the cardiovascular system are investigated in 22 normal males aged 25–40 years. This was part of a battery of reactive tests which included exposure to 90 dB noise and the cold pressor test. The blood pressure responses to glare were normally distributed. Values in terms of mean ± S.D. were as follows: maximum during glare 119±13·6/90·5 ± 13·7mmHg, mean during glare 114·2±12·2/86·0±12·4, maximum rise 9·5±7·8/13[mddot]7± 10·65 and mean change 4·2±6·0/8·7± 10·2. The maximum rise and mean change in both systolic and diastolic blood pressure differed very significantly from the immediately preceding baseline values. The maximal blood pressure response during glare did not differ significantly from that during exposure to noise or cold. Glare, however, elicited a significantly greater mean change in both systolic and diastolic blood pressure compared with noise. We conclude that exposure to an impulsive glare of car headlight intensity is stressful an...

Pulmonary Involvement in Mixed Connective Tissue Disease

To determine the frequency of pulmonary function abnormalities in mixed connective tissue disease (MCTD), we studied 16 consecutive patients. Spirometry, total lung capacity (TLC), diffusing capacity (Dco), static lung compliance (Cst), and tests of respiratory muscle function (peak inspiratory pressure [PIP] and the maximum change in transdiaphragmatic pressure [delta PDI] during a diaphragmatic Müeller maneuver) were obtained. Airway resistance (RAW) and frequency dependence of compliance were also measured. Static lung compliance was less than 0.2 L/cm H2O in four of nine patients. The PIP was less than 75 cm H2O in only one patient and delta PDI was greater than 45 cm H2O in all ten patients evaluated. Frequency dependence of compliance was abnormal in seven of ten patients, whereas RAW was increased in only three of eight patients. The TLC and DCO were less than 80 percent of the predicted values in ten of 16 and 14 of 16 patients respectively. There was no correlation between the level of extractable nuclear antigen and pulmonary function abnormalities. The study did not identify significant abnormalities in respiratory muscle function.

Effects of environmental control on pulmonary function of horses affected with chronic obstructive pulmonary disease.

The effects of environmental control on horses affected with chronic obstructive pulmonary disease was assessed by clinical examination and pulmonary function tests, ie, maximum change in intrathoracic pressure, tidal volume, minute volume, non-elastic work of breathing, dynamic compliance, inspiratory and expiratory flow rates and arterial blood gas analysis. A controlled environment (ie, bedding horses on shredded paper and feeding a complete cubed diet) caused symptomatic COPD affected horses to become asymptomatic within four to 24 days (mean +/- sd 8.4 +/- 4.8 days). When asymptomatic, their pulmonary function values did not differ significantly from those of normal horses, which indicates that the pathophysiological changes occurring in equine COPD are reversible. The time taken for horses to become asymptomatic correlated significantly with age, duration of illness and severity of disease as adjudged by the non-elastic work of breathing.

Influence of perfusate PO2 on hypoxic pulmonary vasoconstriction in rats.

The purpose of these studies was to evaluate the influence of perfusate oxygen tension on hypoxic pulmonary vasoconstriction and to identify the site at which both alveolar and perfusate gas tensions stimulate hypoxic pulmonary vasoconstriction. Lungs from adult rats were ventilated and perfused in vitro at constant temperature, PCO2, and pH, with a perfusion circuit incorporating a membrane oxygenator that allowed independent control of the alveolar and perfusate gas tensions. Blood flow to the lung was constant (0.06 ml per g body weight per min), and pulmonary vascular resistance was therefore proportional to pulmonary artery pressure. In study 1, the pulmonary artery pressor response to zero or 22 mm Hg alveolar oxygen was measured when the perfusate oxygen tensions were approximately 8, 26, 41, 64, or 128 mm Hg. The pressor response as a percent of the maximum pressure change was progressively reduced as perfusate oxygen tension increased. For alveolar oxygen tension of zero; the pressor response = 128 -39 (Log PPO2) and r = 0.8 (P less than 0.01), the effect of perfusate gas tension on the response to alveolar gas tension of 22 mm Hg was similar. These results demonstrate that the stimulus for hypoxic pulmonary vasoconstriction is a function of both alveolar and perfusate oxygen tension. In study 2, the response to alveolar oxygen tension of 42 mm Hg was measured with mean perfusate oxygen tensions of 130, 52, and 17 mm Hg. In six animals with forward perfusion, the responses decreased with increasing perfusate oxygen tension, as in study 1. In another six animals, with retrograde perfusion, the responses to alveolar hypoxia were not altered when perfusate oxygen tension was increased. These results demonstrate that the sensor region for hypoxic pulmonary vasoconstriction is precapillary. These studies confirm and extend previous hypotheses that alveolar and perfusate oxygen tensions together, determine the PO2 at a precapillary site to stimulate hypoxic pulmonary vasoconstriction.

A pressure curve monitor for intratracheal jet ventilation

Most of the complications during intratracheal jet ventilation for laryngomicroscopy are due to the unnoticed wearing off of laryngeal muscle relaxation. Recovering laryngeal muscle function will, by slightly narrowing the size of the glottis, influence the slope of the quickly rising part of the pressure curve, when influences on maximum airway pressure are still not detectable. An electronic device incorporating the window comparator technique monitors the pressure curve and sets off an alarm before changes in maximum airway pressure or recovery of muscle strength in the forearm are detectable. The pressure curve monitor could be useful also with intratracheal jet ventilation for treating adult respiratory deficiency and with conventional ventilators during anaesthesia to detect the wearing off of muscle relaxation.

Cholinergic actions of false neurotransmitters: Acetyldiethylcholine

Acetyldiethylcholine (AcDECh), a false transmitter at cholinergic synapses, binds to central muscarinic receptors with 14-fold lower affinity than acetylcholine (AcCh). The properties of this binding, including the limited extent of regional specificity and binding activation of N-ethyl-maleimide, are those associated with weak agonists and antagonists, intracerebroventricular injection of AcDECh or AcCh produces an increase in arterial blood pressure which is blocked by prior administration of atropine (10 nmol). While AcDECh is 17-fold less potent than AcCh in producing the pressor response, the maximum pressure changes and time courses are comparable. AcDECh also binds to nicotinic receptors of Torpedo electric organs thereby inducing conformational changes in the receptor-ion channel complex that are associated with postsynaptic activation. In these nicotinic actions, however, AcDECh is 320-fold less active than AcCh.