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Biomedical subjects

J Timisjärvi

Publications and source records attributed to J Timisjärvi.

At least 19 recordsLinked to original sources
PubMed2000

Effects on dogs of surface-induced hypothermia and rewarming on the right heart function and pulmonary circulation.

Hypothermia is commonly found in accidents on land and at sea, yet its pulmonary circulatory effects have not been studied before. To study the effects of hypothermia on the right heart function and pulmonary circulation, cardiac catheterization was carried out on nine anaesthetized beagle dogs. The dogs were cooled between ice bags until the temperature in the pulmonary artery was 25 degrees C and then rewarmed using a heating box especially constructed for this purpose. Heart rate decreased significantly (P < 0.01) during cooling. Cardiac output also diminished mainly because of decreased heart rate. Total pulmonary resistance increased in the cold (P < 0.05) and returned to the initial level during rewarming. The peak rate of increase in pressure (dP/dtmax) of the right ventricular pressure curve did not show any significant change. Retardation in relaxation in hypothermia was indicated by an increase (P < 0.01) in the peak negative dP/dt of the right ventricular pressure curve. According to our results, the contraction rate did not change, but the relaxation rate decreased significantly during cooling. No signs of heart failure were observed and all parameters returned to normal during rewarming. In conclusion, right ventricular function was not compromised even during deep hypothermia.

Animals↗
PubMed2000

Effects of seasonal photoperiod on serum 25-hydroxycholecalciferol and calcium in reindeer, Rangifer tarandus tarandus.

In order to understand the effects of solar irradiance on calcium metabolism we measured serum 25-hydroxycholecalciferol and total calcium levels monthly in 6 female nonpregnant reindeer maintained in the Oulu area (65 degrees N). Mean monthly serum total calcium levels varied slightly and the highest levels were seen in October. Serum 25-hydroxycholecalciferol levels were highest in October but the monthly variation was also slight. The small monthly variation of the analytes' abundance and the fact that they peaked not until 4 months after the longest day, (i.e. the main stimulus for vitamin D synthesis) could have something to do with the supplementation of this vitamin in the diet of the captive reindeer.

Animals↗
PubMed1999

Annual serum PICP and ICTP and antler growth in female reindeer (Rangifer tarandus tarandus).

Annual cycle of type I collagen formation and degradation and antler growth was studied in six adult female reindeer, Rangifer tarandus tarandus. Blood samples were collected twice a week during 1 year. Antler length was measured weekly during the antler growth period. An assay for human PICP, the carboxyterminal propeptide of type I procollagen, was used as an indicator of type I collagen formation and an assay for bovine ICTP, the carboxyterminal telopeptide of type I collagen, as an indicator of type I collagen degradation. PICP was clearly increased during the antler growth period. Also ICTP was slightly elevated during antler growth, but the highest values were found in autumn and winter. Our statistical analysis revealed that changes in lagged values (from 3 to 6 weeks) of PICP could be linked to the subsequent changes in the growth rate of the antler, although the highest values of PICP were found during the final third of antler growth. ICTP had significant predictive power as well, but the connection with the growth rate seemed more immediate than that of PICP. In conclusion, antler collagen synthesis can be predicted by PICP, but also ICTP was related to the antler growth.

Animals↗
PubMed1997

Effects of surface-induced hypothermia and rewarming on canine cardiac contraction-relaxation cycle.

The aims of this study were to elucidate the effects of cooling and rewarming on cardiac contraction-relaxation cycle. Cardiac catheterization was carried out on eleven anaesthetized beagle dogs. The dogs were cooled between icebags until the temperature of the blood in the ascending aorta was 25 degrees C and then rewarmed. Heart rate increased transiently at the beginning of cooling down to 33 degrees C (P < 0.05). Cardiac output first tended to increase until a body temperature of 33 degrees C was achieved but then decreased (P < 0.05). The systolic period lengthened significantly (P < 0.001) when the body temperature decreased from 37 degrees C to 25 degrees C. Cardiac relaxation slowed down linearly with temperature during cooling. The peak value of the first order derivative of the ventricular pressure curve (dP/dtmax) increased at the beginning of cooling down to 33 degrees C, indicating enhanced systolic pressure rise in left ventricle but returned to baseline values at lower temperatures. However the ejection fraction, systolic period and the systemic vascular resistance increased at the temperatures below 33 degrees C despite the unaltered peak dP/dt and thus we conclude that the contraction force is augmented in the hypothermia. All the parameters measured recovered to normal during rewarming and no signs of heart failure were noted during the experiments.

Animals↗
PubMed1994

Annual variations in serum thyroid-stimulating hormone and thyroid hormones and in their responses to thyrotrophin-releasing hormone in the reindeer.

The reindeer in its natural habitat is subject to great annual variations in ambient temperature, illumination and nutrition. To ascertain the effect of these environmental factors on thyroid function, serum thyroid-stimulating hormone (TSH), thyroxine (T4), tri-iodothyronine (T3) and reverse T3 (rT3) concentrations were measured four times a year (2 June, 8 October, 21 November, and 24 February) in 14 animals housed outdoors at latitude 69 degrees 10'N. They all showed statistically significant (P < 0.05) seasonal changes. Serum TSH and T4 were highest in February (623 +/- 30 ng/ml and 287 +/- 19 nmol/l respectively). TSH was lowest in October (318 +/- 47 ng/ml) and T4 in November (199 +/- 19 nmol/l). The T3 concentration was highest in November (3.0 +/- 0.3 nmol/l) and lowest in June (1.8 +/- 0.2 nmol/l). In contrast, rT3 was highest in June (3.6 +/- 1.2 nmol/l) and lowest in November (1.9 +/- 0.6 nmol/l). Thus, there was an inverse relationship between T3 and rT3 (linear regression r = -0.406, P < 0.01). TSH, T4, T3 and rT3 responses to exogenous thyrotrophin-releasing hormone (synthetic TRH; 500 micrograms i.m.) were determined in ten animals. The magnitude of their response to TRH was significantly (P < 0.05) dependent on the time of year. When compared with the control level all the parameters rose significantly (P < 0.05). The greatest rise in serum TSH occurred in October (219 +/- 151%) and the smallest in February (66 +/- 53%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Nutritional Physiological Phenomena↗
PubMed1994

Thermal properties of thermodilution catheters.

A suitability of thermodilution catheters to hypothermic conditions was investigated. Thermal properties of two types of thermodilution catheters (Edwards and Spectramed) were checked within a temperature range of 37 degrees C to 22 degrees C. The linear calibration method normally used in normothermia appeared to be inadequate because of the non-linear character of the temperature-resistance curve of the thermistor probe. The best calibration was obtained by using second order formula (ax2 + bx + c) that was fitted to measured temperature-resistance points. An exponential calibration was also tested, but the correlation of the fit was not as good than in the case of the polynome. The absolute variation of resistance of catheters at 37 degrees C was large. If the catheters are calibrated according to mean values, the error in temperature determination was about 1 degree C at normothermia. Erroneously measured temperatures in hypothermia give false cardiac output measurements, which can be dangerous in clinical practice.

Catheterization↗
PubMed1992

Seasonal and daily patterns in melatonin secretion in female reindeer and their calves.

Daily patterns of pineal function were studied in different seasons in 10 adult semidomesticated female reindeer and 5 prepubertal calves living in a natural arctic environment at latitude 69 degrees 10'N. Serum samples for melatonin RIA were collected every 4 h for 24 h in October (10 h of light, 14 h of darkness and 8 h of light, 16 h of darkness), December (24 h of darkness), March (13 h of light, 11 h of darkness), and June (24 h of light). A significant daily variation in serum melatonin levels was observed in the adult reindeer, with peak values (20-50 ng/liter) occurring during the night in autumn, winter, and spring, but not summer. The daytime values at 13 h (5-10 ng/liter) were constant throughout the year. Total daily amounts of melatonin, the duration of peak levels, and maximal concentrations were significantly lower in spring and summer than before the rut in autumn. The exposure of adult animals to artificial darkness from bright sunlight on August 1 and September 21 resulted in an immediate increase in serum melatonin concentrations. The 2-week-old calves had detectable serum melatonin levels, but no daily rhythm in the spring, whereas a rhythm was detectable by the first autumn, only to disappear unexpectedly during the first winter and return in the spring. At the age of 16 months, the calves had serum melatonin concentrations similar to those in the adults. Our present results show that the continuous illumination experienced during the summer abolished the normal daily melatonin rhythm. This does not seem to be related to organic changes in the pineal gland, since exposure to darkness during the summer increased melatonin levels. The highest melatonin secretion occurred in the autumn and was evidently associated with the rut. Similarly, the daily melatonin rhythm of an adult type observed in the calves at the age of 16 months may be related to the observation that most calves were in rut. Thus, a high rhythmical melatonin secretion appears to relate to puberty and the initiation of heat in female reindeer.

Animals↗
PubMed1991

Cardiac function in hypothermia.

Hypothermia retards cardiac contraction and prolongs the subphases of the cardiac cycle in varying degrees. Six anaesthetized beagle dogs were catheterized and cooled between ice bags until the aortic blood temperature was 25 degrees C and then rewarmed to normothermia. The speed of relaxation decreased to a half from its value in normothermia as indicated by the time constant of exponential isovolumic ventricular pressure fall and by the change in the negative dp/dt. It is suggested that retardation of relaxation is connected with temperature dependent changes in calcium kinetics. Decrease of cardiac output was mediated mainly by decreased stroke volume indicating sympathetic tone in spite of cold narcosis.

Animals↗
PubMed1987

Anabolic steroids alter the haemodynamic effects of endurance training on the canine left ventricle.

The effects of six week, high-dose anabolic steroid treatment (methandienone, 1.5 mg/kg/day) on the changes in left ventricular function induced in dogs by endurance training were studied by a catheterization technique under anaesthesia. Pacing, isoproterenol and dextran infusions were used as loading tests (respectively). Dogs were randomized into an exercise group (EG, n = 7) and an exercise-steroid group (ESG, n = 7), the latter receiving anabolic steroids as well as participating in the training program. In a standardized submaximal exercise test, the heart rate of unanesthetized dogs was lower both in the EG (p less than 0.001) and in the ESG (p less than 0.01) after the training period than before it. In the EG the resting systemic vascular resistance (SVR) before haemodynamic interventions was lower (p less than 0.05) and left ventricular stroke work (SW) was higher (p less than 0.05) after the training period than before. In the ESG, left ventricular ejection fraction (EF) decreased with training and anabolic steroid treatment (p less than 0.05). After the training period isoproterenol increased the maximum velocity of the cardiac contractile element significantly more (p less than 0.05) in the EG than in the ESG. Also SW increased in the EG (29%, p less than 0.001), but not in the ESG (-11%, NS). Endurance training increased the left ventricular end-diastolic and stroke volumes during isoproterenol infusion, but this training effect was attenuated by simultaneous anabolic steroid treatment (p less than 0.05 between the groups in both cases). During the isoproterenol test SVR decreased less in ESG than in EG (p less than 0.05 between).(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic Agents↗
PubMed1986

Time constant of isovolumic pressure fall in the intact canine left ventricle.

The two standard methods of computation of the time constant of the isovolumic single exponential decay of the left ventricular pressure were compared in anaesthetised, artificially ventilated, closed chest dogs in 87 experiments. In 23 additional experiments, carried out under basal steady state conditions, the time constant attained a mean (SD) value of 32(5) ms when computed according to the method with zero pressure asymptote assumption (Tz) and 39(7) ms when estimated according to a fit with variable pressure asymptote (Tv). Phenylephrine infusion significantly prolonged Tz from 31(6) to 46(12) and Tv from 39(7) to 92(52) ms. The increase in Tv was significantly greater than that in Tz. Propranolol increased Tv by 50% but Tz remained unaltered. Isoproterenol significantly decreased Tz from 33(2) to 18(3) and Tv from 38(3) to 29(3) ms. The decrease in Tz was significantly greater than that in Tv. Calcium chloride and atrial pacing decreased time constants, but volume loading by dextran infusion did not affect them. With regard to the whole material, the linear regression analysis yielded 0.776 as the coefficient of correlation between Tz and Tv. The two methods of time constant calculation appeared to diverge significantly always when changes in afterload or sympathetic activity were involved. These results indicate the dependence of relaxation on afterload but the independence on preload or ejection timing. In the light of these results the zero pressure asymptote method is recommended for the time constant computation as the practical choice when relaxation of the intact left ventricle is assessed.

Animals↗
PubMed1986

The automatic computation of pressure-derived maximal shortening velocity (Vmax) of the unloaded contractile element in the intact canine heart left ventricle.

Estimation of the maximum velocity (Vmax) of the contractile element of the intact left ventricular wall muscle demands extrapolation of the force-velocity curve to zero load. The present paper describes our on-line computation system for measuring and analysing pressure derived Vmax using both linear (Vmax-lin) and exponential (Vmax-exp) extrapolation methods. The developed pressure during isovolumetric phase of systole was used as an equivalent of the force. Testing on anaesthetized artificially ventilated dogs showed the exponential function to fit pressure-velocity data better than the straight line did. The Vmax-exp attained 15-35% greater values than Vmax-lin, but both responded almost equally when considered on the basis of linear regression analysis (r = 0.991, n = 725). Changes of contractility caused by i.v. infusion of isoproterenol, calcium chloride or propranolol were practically similar when assessed by either method of Vmax computation, or by dP/dtmax. Volume loading by dextran infusion increased not only dP/dtmax, by 33 +/- 13%, but also Vmax, up to 24 +/-. When arterial pressure was raised by phenylephrine infusion, or heart rate by atrial pacing, dP/dtmax increased significantly while Vmax remained unaltered. Hence, the linear and exponential dP/dtmax increased significantly while Vmax remained unaltered. Hence, the linear and exponential extrapolation procedures provided comparable values for Vmax, but the linear one due to its simplicity is more suited for on-line computation. The Vmax thus obtained is, however, not independent of the changes in preload.

Animals↗
PubMed1985

Electromechanical delay in the intact dog heart.

A computer method was developed for the determination of electromechanical delay defined as the time between the onset of Q-wave and the onset of the left ventricular systolic pressure rise. It was validated for heart catheterization studies on 56 intact anaesthetized beagle dogs in 86 sessions. The mean basal value of the electromechanical delay was 22 +/- 4 msec. Heart rate, contractility, preload and afterload were changed by atrial pacing and by infusions of calcium chloride, isoproterenol, propranolol, dextran and phenylephrine. Increase of heart rate by pacing from the spontaneous rate of 90 per min to 240 per min prolonged the electromechanical delay from 21 +/- 5 to 33 +/- 14 msec (P less than 0.001). Otherwise the duration of electromechanical delay changed independently of the heart rate. If it changed, the direction of the change followed that of the pre-ejection period. Its proportion of the pre-ejection period varied from 26 to 52%. The electromechanical delay shortened when a positive inotropic effect was noticed or the presystolic fibre length increased.

Animals↗
PubMed1984

The structure and insulation properties of the reindeer fur.

The structure of the fur of the reindeer (6 adults, 4 calves) was studied with light and scanning electron microscopy and skin and rectal temperatures were measured in 216 living animals at varying ambient temperatures (-28 to +15 degrees C) and also on excised skin samples in the laboratory (temperature range -20 to +20 degrees C, wind 0 or 10 m/sec, 5 different directions). Guard hair count and length varied according to the site of excision and were on average 2000/cm2 and 12 mm on the foreleg, 1000/cm2 and 30 mm on the abdomen and 1700/cm2 and 30 mm on the back. The corresponding counts in the calves were higher but the hairs were shorter. The rectal temperatures ranged from 38 to 40 degrees C independently of the ambient temperature. The dependence of the skin temperature on the ambient temperature was complex in living animals. The dependence was strongest in the legs. The skin temperature of the excised samples depended rather linearly on the ambient temperature. It is concluded that the reindeer can maintain its body temperature also in severe cold although the extremities show characteristics of heterothermia.

Aging↗
PubMed1984

Haemodynamic effects of precordial or carotid ultrasound application on the dog.

Ultrasound (1.09 MHz, 1 to 2 W/cm2) was applied on the thoracic wall or on the neck of the anaesthetized, artificially ventilated dog. The heart rate, stroke volume and cardiac output remained almost unchanged during both applications. The aortic and pulmonary arterial pressures increased by 7 to 9 mmHg. Pulmonary arterial wedge pressure increased. The right atrial mean and aortic and pulmonary arterial pulse pressures did not change. The observed changes except the rise of wedge pressure returned to the control values within 5 min after the application. The present findings suggest an increase in systemic vascular and pulmonary arterial resistances in connection with both methods of ultrasound application. The precordial application was associated with pooling of blood in the pulmonary circuit. Since the ultrasound non-selectively affects several receptors and structures the final role of the sympathetic nervous system can be evaluated after experiments with isolated targets and selected denervations.

Animals↗
PubMed1984

The immediate haemodynamic effects of MPV 295 (4(5)-2-(2,6-dimethylphenyl)ethylimidazole), a new vasoactive agent with alpha-adrenoceptor agonistic properties, in the anaesthetized dog.

We have evaluated the immediate (0-30 min) circulatory effects of an i.v. bolus of a new compound, MPV 295, an imidazole derivative (1 to 120 micrograms/kg of b.w.) on anaesthetized (morphine, pentobarbital), normotensive, artificially ventilated beagle dogs using catheterization technique. MPV 295 firstly raised and then decreased aortic pressures at dose 30 micrograms/kg. Systolic pressure decreased also at doses 15 and 60 micrograms/kg. Heart rate and cardiac output decreased but the change in cardiac output was significant only at dose 30 micrograms/kg. Peripheral vascular resistance increased. Pulmonary arterial systolic pressure decreased at dose 15 micrograms/kg but did not respond significantly to other doses. In conclusion, MPV 295 exerted an initial sympathomimetic action which was followed by hypotensive effect with the former being peripheral and the latter central in origin. It showed a narrow dosage range for the hypotensive action and, like clonidine, appeared to be an alpha 2-agonist in qualification experiments.

Adrenergic alpha-Agonists↗
PubMed1984

Stewart-Hamilton and gamma variate methods in computer analysis of dye curves.

The conventional Stewart-Hamilton (SH) principle was compared to the gamma variate function fitting (G) method in on-line computer determination of cardiac output from dye dilution curves on anaesthetized animals (dogs, cats and reindeer), and on an artificial circulation model with known flows. In animal experiments, indicator was injected into the pulmonary artery (n = 674), the coefficient of linear correlation (Rlin) between G and SH was 0.982, and the regression line of G was 1.101 x SH-0.072 l/min. When the right atrium was the site of indicator injection (n = 88), Rlin was 0.982, and the regression line nearly agreed with the line of unity. In the artificial circulation model with the single circulation arrangement (n = 81), Rlin between SH and known flow (Q) was 0.959, and between G and Q it was 0.951; both methods over-estimated the flows, with the over-estimation being greater in the case of G. In the artificial model with recirculation effect (n = 31), Rlin between SH and Q was 0.953, and between G and Q 0.942, G again over-estimating the real flow essentially more than SH. Thus, in most cases the Stewart-Hamilton principle seems to be the more reliable way of analysis of dye dilution curves also in modern computer practice.

Anesthetics↗
PubMed1984

The responses of the systemic and pulmonary circulations to intravenously administered clonidine in anaesthetized dogs.

We have studied the immediate (0 to 30 min) effects of an i.v. bolus of clonidine (0.5, 1, 3, 5, 7, 10, and 15 micrograms/kg of b.w.) on systemic and pulmonary haemodynamics in anaesthetized (morphine, pentobarbital), artificially ventilated, normotensive beagle dogs. Clonidine initially raised and then decreased aortic pressures in a dose-dependent manner except in the case of dose 10 micrograms/kg when only a rise was observed. The effects on pulmonary arterial pressures were less consistent, and only at doses 3 to 5 micrograms/kg was the clear diphasic response pattern recognized. Heart rate and cardiac output decreased. Systemic vascular and pulmonary arterial resistances increased with the greatest increase soon after administration of the drug administration. Right atrial and pulmonary arterial wedge pressures increased. Additionally, we explored the effects of atropine with and without clonidine, which were increase in heart rate, cardiac output and aortic pressures but a decrease in right atrial and pulmonary arterial wedge pressures. It was concluded that clonidine induces a dose-dependent vasoconstriction in both systemic and pulmonary circulations, and pressure changes, thus, depend on peripheral vasomotion and flow. Atropine restores heart rate and also partially flow, but cannot abolish clonidine induced vasoconstriction.

Animals↗