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Biomedical subjects

M Hakumäki

Publications and source records attributed to M Hakumäki.

9 recordsLinked to original sources
PubMed2006

Role of cage material, working style and hearing sensitivity in perception of animal care noise.

During daily care, laboratory animals are exposed to a variety of sounds which may have effects on welfare and also cause physiological and behavioural changes. So far, almost no attention has been paid to individual sounds or the sound level caused by animal care or the sound level inside the animal cage. In this study, sounds from selected rat care procedures were recorded: pulling cage out of the rack, placing it onto a table and replacing the cage back into the rack; with measurements made inside the rat cage and in the adjacent cage. Diet was poured into the food hopper and sounds were recorded inside the cage and also the adjacent cage. The work was repeated in a calm and also in a hurried style, using stainless steel and polycarbonate cages. Finally, the sounds produced by running tap water were recorded. Differences between rat and human hearing were compared using novel species-specific sound level weightings: R-weighting for rats dB(R) and H-weighting for human dB(H). Hurried work with steel caused sound exposure levels exceeding 90 dB(R) when the cages were placed into the rack and about 80 dB(R) when pulling them out of the rack or placing onto a table. With polycarbonate, the levels were 10-15 dB(R) lower. Unhurried calm working produced lower sound exposure levels than hurried working in many procedures. When the procedures were repeated with measurements in the adjacent cage, the sound exposure levels were lower, but the results were similar. Pouring food pellets into a hopper above the rat's head caused 15 dB(R) higher sound exposure levels than pouring food to an adjacent cage. In general, humans hear these sounds about 10-15 dB louder than rats. In conclusion, cage material, working style and hearing sensitivity all have an impact on the sound exposure level in the rodent cage. With correct working methods, high sound levels can be efficiently avoided in most cases.

Animal Welfare↗
PubMed2000

R-weighting provides better estimation for rat hearing sensitivity.

Since sounds may induce physiological and behavioural changes in animals, it is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not take account of hearing sensitivity-which may differ widely both between and within species at various frequencies-the results may be spurious. In this study a novel sound pressure level weighting for rats, R-weighting, was calculated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the response curves of two different loudspeakers. The sound signal resulted in different sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound levels were lower. With a middle-range loudspeaker, unable to reproduce high frequencies, R-weighted sound showed the lowest sound levels. In conclusion, without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that intended. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a necessity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommended.

Acoustics↗
PubMed1990

Haemodynamic information encoded in the aortic baroreceptor discharge during haemorrhage.

This study concerns the function of aortic baroreceptors during slow haemorrhage, in particular the mechanisms by which baroreceptors respond to hypovolaemia in the absence of hypotension and the manner in which haemodynamic information is encoded in the aortic nerve discharge. Beagle dogs, anaesthetized with morphine and chloralose, were instrumented for the recording of aortic pressure, aortic diameter, aortic flow and aortic nerve activity. The animals were subjected to slow haemorrhage (0.4 ml kg-1 min-1) of 20% of the estimated blood volume. Mean aortic pressure remained unchanged, whereas mean aortic diameter, mean aortic tension and aortic baroreceptor activity decreased during the haemorrhage. Baroreceptor sensitivity to mean aortic pressure, mean aortic diameter and mean aortic tension decreased as the haemorrhage proceeded. Also, the sensitivity of baroreceptors to mean aortic pressure and mean aortic diameter during acute pressure stimulation was attenuated. The results indicate that during non-hypotensive haemorrhage aortic baroreceptor discharge is reduced by two mechanisms: firstly, via constriction and stiffening of aortic smooth muscle and, secondly, via direct effects of the compensatory mechanisms on the baroreceptors. The reduced sensitivity renders the baroreceptors capable of responding to hypovolaemia prior to the onset of hypotension. In the regression analysis, systolic aortic diameter proved to be the best determinant of baroreceptor activity (r = 0.877). Of the neural variables, impulses per cardiac cycle and average discharge rate were the most reliable, but no difference in the relative importance of these two parameters could be observed.

Acid-Base Equilibrium↗
PubMed1989

Effect of acute intravenous volume loading on haemodynamics and aortic baroreceptor activity in dogs.

This study evaluates the effect of acute intravenous volume loading on haemodynamics and aortic baroreceptor activity in order to determine the mechanistic factors responsible for divergent heart rate responses to volume loading. Eleven beagles were anaesthetized and instrumented for the recording of aortic pressure, diameter, flow and aortic baroreceptor activity. Isotonic saline, equal to 20% of the estimated blood volume, was infused intravenously within 60-90 s. The animals were divided into tachycardiac and bradycardic groups according to their heart rate response to volume loading. In the group developing the tachycardic response, aortic baroreceptor activity increased. Total peripheral resistance was reduced by 31% and variables representing aortic stretch, mean aortic pressure, diameter and tension remained unchanged. In contrast, in the group developing the bradycardiac response, aortic baroreceptor activity increased markedly. Also in this group peripheral resistance decreased, but only by 15%, which was significantly less than in the tachycardiac group. Factors determining aortic stretch, mean aortic pressure, diameter and tension also increased significantly. Earlier studies show that regardless of the resulting heart rate response, atrial receptor activity increases during volume loading. Thus, we conclude that during cardiac acceleration, marked peripheral vasodilation eliminates the stimulation of baroreceptors and therefore the tachycardic response caused by atrial receptors develops. In the case of cardiac slowing, vasodilation also takes place, but is not sufficient to prevent activation of baroreceptors. In consequence, increased baroreceptor activity overrides the tachycardic drive coming from the atrial receptors and a typical baroreceptor reflex becomes manifested.

Animals↗
PubMed1987

Combined effect of low doses of propranolol and ethanol on cardiac function: a comparative study by radionuclide ventriculography in conscious dogs.

Trained, chronically instrumented, conscious dogs were used to evaluate the effect of propranolol (PRO), ethanol (ETH) or their combination (P + E) on the left ventricular (LV) function by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m diethylenetriamine pentaacetic acid via the catheter to the left atrium. The data was collected for 12 sec. to a computer by frame rate of 20 frames/sec. from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60-degree head-up tilted positions. After control measurements the data were obtained with 0.5 mg/kg of PRO, 0.45 g/kg of ETH and their combination. The P + E combination increased significantly LV end-diastolic and end-systolic volumes, whereas LV peak ejection rate and ejection fraction were decreased. Upright position diminished the LV volume and increased heart rate, while ejection fraction and cardiac output remained unchanged. The first-pass RNV method proved to be promising for measuring the cardiac pharmacological effects in conscious dogs. The combination of propranolol and ethanol in low doses induced an unexpectedly strong depression of LV function, which is supposed to be followed of latent cardiac depressing effect of ETH revealed by blockade of compensatory adrenergic mechanisms with PRO.

Animals↗
PubMed1987

First-pass radionuclide ventriculography in conscious dogs.

Trained, chronically instrumented, conscious dogs were used to study the function of the left ventricle by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m-DTPA via the catheter to the left atrium. The data was collected for 12 s to a computer by frame rate of 20 frames/s from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60 degrees head-up tilted positions. The measurements were done with two injection volumes (0.25 and 1.0 ml/kg) to study the effect of volume on the results. The body position had effect on left ventricular end-diastolic and stroke volumes, whereas ejection fraction remained unchanged. In comparison of the two injection volumes a minor difference was found in left atrial emptying, while the differences in left ventricular function were non-significant. In spite of training and careful standardization of experimental procedures, relatively high individual variation between animals was found in most parameters studied. The first-pass RNV method proved to be promising for measuring the left ventricular function in conscious dogs. Although the left atrium has reflectory tachycardic potential to distension, the volumes used for RNV did not affect the results. The left ventricular adaptation to head-up tilting in conscious dogs seems to consist mainly of decrease in left ventricular volume without significant effect on ejection fraction.

Animals↗
PubMed1979

Blood flow in proximal femur of the dog determined by the local 133Xe injection method.

A new approach for measuring blood flow in bone is presented. It consists of the local injection of 133Xe into the proximal femur of adult beagles and the external measurement of isotope washout curves. The curves were analyzed using a two-compartment exponential model. The half-times for the tracer washout from the fast and slow compartment were 3.34 +/- 0.48 min and 33.6 +/- 11.7 min (mean +/- 1 S.D.) respectively. Blood flow was calculated using a measured blood to bone partition coefficient of 1.55 ml/g. The mean blood perfusion in proximal femur of the dog was 10.8 +/- 4.3 ml/100 g/min (mean +/- 1 S.D.). This value agrees well with most estimates of bone circulation. Due to rapid disappearance of 133Xe the method is easy to repeat and is thus suitable for physiological studies of local blood flow in bones.

Animals↗