A comparative study of invasive and oscillometric methods of arterial blood pressure measurement in the anesthetized rabbit

INTRODUCTION

The aim of this project was to evaluate the reliability and accuracy of direct, using the central ear artery (CEA), and oscillometric, using limb-cuffs, methods of arterial blood pressure (AP) measurement in the anesthetized rabbit.

METHODS

New Zealand rabbits were anesthetized using a xylazine-ketamine-isoflurane protocol. Using the abdominal aorta (ABA) as direct "gold standard" for AP measurements, ABA pressure readings, via femoral artery catheterization, were compared with those made simultaneously from the ascending aorta after median sternotomy. Thereafter, direct CEA as well as forelimb-(FL) and hindlimb-(HL) cuff oscillometric readings were compared with those made simultaneously from ABA.

RESULTS

The blood pressure in the ABA correlated with that from ascending aorta. Furthermore, CEA correlated with the ABA readings. Nevertheless, at high pressures, their divergence from "true" pressure tended to increase. Oscillometric readings at the FL site correlated well with "true" pressure while those at the HL site did not. Their divergence tended to increase at high pressures when using the FL site, while it varied when using the HL site. The accuracy of measurements was moderate for the FL site while poor for the HL site.

DISCUSSION

Our results suggest that the CEA can be readily used with high reliability and accuracy for direct AP measurements in the anesthetized rabbit. On the other hand, the FL-cuff oscillometric method should only be used for the evaluation of AP at low and normal pressure ranges.

[Non-invasive blood pressure measurement in dogs and cats]

Bloodpressure measurements are of interest for todays veterinary practice. It can be used for screening of incoming patients, the emergency case, the intensive care patient and sedated animal. Furthermore, like in human medicine, blood pressure can be influenced by several diseases. The most reliable method of arterial blood pressure measurement is the direct or invasive method. Only the non-invasive methods doppler and oscillometric methods are used in veterinary medicine. The article describes the method of measurement, and provides a review of the literature. The oscillometric method especially in dogs. Both methods measure a lower bloodpressure if compared with an invasive method. The difference in bloodpressure is for the oscillometric method in cats greater then in dogs and appears to increase at higher blood pressures. Keeping these facts in focus, and if one is able to work in a quiet environment, repeat the measurements and maintain a critical attitude, blood pressure measurements can be performed in veterinary practice.

Hypertension in renal disease: Diagnosis and treatment

Hypertension is a common sequela to renal disease in cats and dogs, affecting as many as 61% cats and 93% of dogs, respectively. Undiagnosed and untreated, elevations in blood pressure can have deleterious effects on the brain and heart as well as promote further renal injury. In this article, we discuss the identification of patients at risk for hypertension as well as methods for measuring blood pressure and the treatment of hypertensive patients.

Influence of breathing pattern and lung inflation on impulse oscillometry measurements in horses

The objective of this paper was to determine if changes in ventilation patterns could influence the outcome of respiratory function measurements performed with our impulse oscillometry system (IOS) in horses. In a first study, IOS tests were performed in vitro on six isolated equine lungs. Lung inflation levels were controlled by modifying depressurisation inside an artificial thorax and different ventilation patterns were imposed. In a second in vivo study, transient variations in breathing pattern were evaluated both with the IOS and a current reference technique (CRT) in five healthy mature horses after an intravenous (i.v.) injection of lobeline hydrochloride. In both studies, respiratory rate (RR, range: 7-42 breaths/min.) and tidal volume (V(T), range: 0.4-25 L) had minor or no influence on IOS parameters. The influence of lung inflation, most marked for resistance at 5 Hz (R(5 Hz)), was limited for the considered physiological range. In vivo, statistical models indicated that maximal changes in pleural pressure (Max Delta Ppl) and peak flows were the main determinants of the variability of the resistance (R(rs)) and the reactance (X(rs)) of the respiratory system. The fourfold increase in baseline Max Delta Ppl and peak flows obtained during hyperpnoea caused a significant increase in R(rs) at 5 and 10 Hz and a decrease in X(rs) at all frequencies. We conclude that IOS parameters are not influenced by tachypnoea, but will reflect alterations in respiratory mechanics caused by hyperpnoeic breathing.

Respiratory mechanics in conscious swine: effects of face mask, head position and bronchoconstriction evaluated by impulse oscillometry

Airway obstruction in pigs (sedated or non-sedated) fixed in a sling was studied using impulse oscillometry (IOS). (i) Vertical flexion of the pig's head was used to simulate an artificial obstruction of the upper airways. (ii) Bronchial obstruction was induced by inhaling differing quantities of an aerosol produced from 0.33% carbachol solution. The ventilatory pattern was examined by measuring respiratory rate (RR) and tidal volume (V(t)). To evaluate respiratory mechanics, impedance parameters resistance (R) and reactance (X) as well as coherence (Co) were examined, each at frequencies of 5, 10, 15, 20, 25 and 35 Hz. Using a simple 7-element-model introduced by J. Mead [Physiological Review 41 (1961) 281], distal respiratory resistance (R(dist)), proximal airway resistance (R(prox)), and additional shunt compliance (C(a)) of the animal's snout and the air inside the facemask were evaluated. By fitting this model to the primary measured impedance spectra, the influence of the face mask could be eliminated in the model calculation to allow assessment of the real respiratory impedance. This recalculation made clear that the facemask had an influence on the spectral course of R and X, depending on the clinical situation, and the upper frequency range was altered the most. Under conditions of (i) upper airway obstruction, especially the X values were distorted by facemask almost over the whole frequency range. Once the data were corrected for the mask, resistance was increased across all frequencies by a fixed amount while reactance was not affected. Under (ii) bronchial airway obstruction (bronchospasm) caused the resistance spectrum to be increased mainly in the lower frequency range. This became visible in both, originally measured impedance spectra and spectra after correction of the mask influence. The reactance course (originally measured and recalculated) decreased at all frequencies during bronchospasm. Coherence over the whole frequency range was lowered at both bronchial and upper airway obstruction.

Effect of aerosolized albuterol sulfate on resting energy expenditure determined by use of open-flow indirect calorimetry in horses with recurrent airway obstruction

OBJECTIVE

To evaluate effects of sedation on stability of resistance of the respiratory system (RRS) and measures of resting energy expenditure (REE) by use of open-flow indirect calorimetry (IC) and treatment with aerosolized albuterol on REE in horses with recurrent airway obstruction (RAO).

ANIMALS

9 clinically normal horses and 8 horses with RAO.

PROCEDURE

In phase 1, RRS was measured by using forced oscillometry (FOT) in 5 clinically normal horses before and after sedation with xylazine. In phase 2, REE was measured in 4 clinically normal horses between 20 and 25 minutes and again 35 to 40 minutes after sedation with xylazine. In phase 3, IC was performed between 20 and 25 minutes and FOT was performed between 30 and 35 minutes after xylazine administration in 8 horses with RAO; after administration of 450 microg of albuterol, IC and FOT were repeated.

RESULTS

In phase 1, RRS values were significantly lower 5 and 10 minutes after sedation. In phase 2, diminishing sedation did not significantly affect REE. In phase 3, there was a significant decrease in mean RRS (1.15 +/- 0.25 vs 0.84 +/- 0.14 cm H20/L/s) and REE (30.68 +/- 17.89 vs 27.46 = 16.54 kcal/kg/d) after albuterol administration.

CONCLUSIONS AND CLINICAL RELEVANCE

FOT and IC are useful in obtaining repeatable measurements of RRS and REE, respectively, in sedated horses. Concurrent bronchodilation and decreased REE after albuterol administration suggest that increased work of breathing as a result of airway obstruction may contribute to increased energy demands in horses with RAO.

Comparative diagnostic test characteristics of oscillometric and Doppler ultrasonographic methods in the detection of systolic hypertension in dogs

Comparison of test characteristics allows a clinician to choose the optimal diagnostic test method for an individual patient. This study assessed the comparative test characteristics of noninvasive (NI) blood pressure measurement methods (oscillometric and Doppler) and used this information to develop optimal cutoff values for diagnosis of systolic hypertension in dogs by these NI methods. Simultaneous NI (oscillometric or Doppler methods) and invasive (arterial puncture [AP]) systolic blood pressure (SBP) measurements were obtained prospectively from normal dogs and dogs suspected of having systemic hypertension based on clinical signs. Oscillometric SBP readings were obtained from the distal hind limb (Osc-L, n = 54) or the proximal tail (T. n = 27). Doppler BP measurements were obtained using a forelimb cuff (n = 57). AP-SBP was categorized as hypertensive if > or = 160 mmHg, and sensitivity (Se). specificity (Sp), and likelihood ratios (LR) were calculated for diagnostic cutoff values ranging from 130 to 220 mmHg. Receiver operator characteristic (ROC) curves were analyzed to determine optimal cutoff values for diagnosis of AP-SBP > or = 160 mmHg. Optimal NI SBP cutoff values considered to reflect AP values > or = 160 mmHg were: Osc-L = 160 mmHg (Se: 65%, Sp: 85%. LR = 4.33: 1), Osc-T = 150 mmHg (Se: 84%, Sp: 75%, LR = 3.36: 1), and Doppler = 160 mmHg (Se: 71%,

Indirect arterial blood pressure measurement in nonsedated Irish wolfhounds: reference values for the breed

Arterial blood pressure measurements were obtained from 158 healthy Irish wolfhounds using the oscillometric technique to establish reference values for the breed. In contrast to other sight hounds, Irish wolfhounds have low arterial blood pressure. Mean systolic pressure for the group was 116.0 mm Hg. Mean diastolic pressure was 69.2 mm Hg, and the mean value for mean arterial pressure was 87.8 mm Hg. Blood pressure measurements were higher in older wolfhounds than in young dogs. There was no difference between systolic and mean arterial blood pressures in lateral recumbency compared to standing position. However, diastolic pressure was slightly lower when standing. Calm dogs had lower pressure than anxious wolfhounds. There was a significant interaction between the effects of age, gender, and mood on systolic, diastolic, and mean arterial blood pressure values.

Evaluation of an oscillometric blood pressure monitor for use in anesthetized cats

OBJECTIVE

To determine accuracy of an oscillometric blood pressure monitor used over a wide range of pressures in anesthetized cats.

DESIGN

Prospective study.

ANIMALS

6 healthy cats.

PROCEDURE

4 female cats and 2 male cats that weighed 2.7 to 4.5 kg (5.9 to 9.9 lb) and were 2 to 8 years old were anesthetized. Blood pressure was measured directly with an arterial catheter placed in the right femoral artery and indirectly from the left antebrachium by use of an oscillometric monitor. A series of diastolic arterial pressure (DAP), mean arterial pressure (MAP), and systolic arterial pressure (SAP) measurements were obtained during hypotension, normotension, and hypertension. Values obtained indirectly and directly were compared.

RESULTS

The oscillometric monitor was accurate for DAP and MAP throughout the entire pressure range and met the standards of the Association for the Advancement of Medical Instrumentation (mean +/- SD difference from values obtained directly, < or = 5 +/- 8 mm Hg). The SAP was increasingly underestimated with increasing overall pressure; mean differences from direct measurements were -5.2, -12.1, and -17.7 mm Hg during hypo-, normo-, and hypertension, respectively. Standard deviations for SAP were all < or = 8 mm Hg. The monitor gave readings during all attempts. The direct blood pressure recording system appeared to perform well with neither under- nor overdamping.

CONCLUSIONS AND CLINICAL RELEVANCE

Except for a minor underestimation of SAP during normo- and hypertension, the oscillometric monitor yielded reliable and easily obtainable blood pressure measurements in anesthetized cats.

Comparative evaluation of ultrasonography and lung function testing with the clinical signs and pathology of calves inoculated experimentally with Pasteurella multocida

Seventeen calves were inoculated intratracheally with Pasteurella multocida 0 on three consecutive days with 10 ml of an inoculum containing 10(9) colony forming units/ml per day per calf. Before the first inoculation and 24 hours after the third, each calf was examined non-invasively by means of a clinical examination, chest ultrasonography, and impulse oscillometry to measure the impedance of the respiratory system. The inoculation of P multocida caused fever and a significant increase in respiratory rate and a decrease in tidal volume. There were also significant changes in the ultrasonographic results and in the impedance of the respiratory system. The percentage of the total surface area of the lungs showing pathological changes when the calves were euthanased 48 hours after the third inoculation ranged from 0.4 to 39 per cent. There were statistically significant correlations between the ultrasound scores and the pathological findings and between the ultrasound scores and the respiratory rate and tidal volume. The changes in the impedance of the respiratory system were not correlated with either the ultrasonographic or the pathological findings.

Substrate vibrations during acoustic signalling in the cicada Okanagana rimosa

Males of the North American cicada Okanagana rimosa (Homoptera: Cicadidae, Tibicininae) emit loud airborne acoustic signals for intraspecific communication. Specialised vibratory signals could not be detected; however, the airborne signal induced substrate vibrations. Both auditory and vibratory spectra peak in the range from 7-10 kHz. Thus, the vibrations show similar frequency components to the sound spectrum within biologically relevant distances. These vibratory signals could be important as signals involved in mate localization and perhaps even as the context for the evolution of the ear in a group of parasitoid flies.

Analysis of respiratory mechanics by impulse oscillometry in non-sedated and diazepam-sedated swine

Analysis of respiratory mechanics using impulse oscillometry is applicable to sedated, or non-sedated (trained) pigs when they are fixed in a sling. In this study, the influence of the following sources of variability on measurement results was examined: (i) sedation with diazepam; (ii) body weight of animals (ranging in age: 40 to 102 days); and (iii) time of the measurement (circadian influences). The following parameters were examined: respiratory rate (RR), tidal volume (v(t)), spectral resistance, reactance and coherence, each at 5, 10, 15 and 20 Hz (R5,...R20, X5,...X20, CO5...CO20, respectively), distal respiratory resistance (Rdist), and proximal airway resistance (Rprox). After sedation (using 1.5 mg diazepam per kg body weight), RR and v(t) decreased significantly. There was a significant improvement of CO5, CO10 and CO15. Increase in body weight was strongly correlated to v(t), furthermore to spectral resistance parameters. Impulse oscillometry system (IOS) parameters showed only slight non-significant alterations in dependency on the time of day. In consequence, different sources of variability must be taken into account when performing IOS measurements in swine.

Mechanics of the respiratory system in healthy newborn calves using impulse oscillometry

Arterial blood gases, acid-base balance and respiratory function tests using impulse oscillometry (IOS) were performed on 40 clinically healthy newborn calves during the first 24 hours of life to evaluate their respiratory adaptation to extrauterine life. Gas exchange efficiency of the lung was significantly improved with time and was accompanied by the correction of the mixed acidosis observed at birth and by significant changes in respiratory mechanics. Major changes were detected within the first 6 hours. The significant decrease in resistance (R) and the increase in reactance (X) with time, demonstrate the improvement in respiratory mechanics of both upper and lower airways, and reflect the increase in lung volume, the improved lung tissue elasticity and/or distribution of the ventilation. Respiratory mechanical, arterial blood gases and acid-base balance data provided in this study describe a successful respiratory adaptation to extrauterine life in healthy newborn calves.

Clinical comparison of three methods to measure blood pressure in nonsedated dogs

OBJECTIVE

To determine arterial blood pressure in client-owned dogs, using direct arterial puncture, oscillometry, and Doppler ultrasonography in a clinical setting.

DESIGN

Prospective study.

ANIMALS

8 clinically normal client-owned dogs.

PROCEDURE

Blood pressures of nonsedated dogs were measured simultaneously, using each of the 3 methods. Mean values obtained were compared with published mean values. Ability of noninvasive methods (Doppler ultrasonography and oscillometry) to accurately predict results of the invasive method, and relationships between blood pressure and age, body weight, and degree of patient anxiety were determined.

RESULTS

Calculated ranges of values (mean +/- 2 SD) determined by direct arterial puncture were: systolic pressure, 114 to 194 mm Hg; diastolic pressure, 66 to 102 mm Hg; and mean pressure, 85 to 129 mm Hg. Ranges determined by use of oscillometry were: systolic, 110 to 190 mm Hg; diastolic, 35 to 107 mm Hg; and mean, 78 to 138 mm Hg. Ultrasonographic and oscillometric values did not accurately predict direct values, but mean values of systolic and mean pressures were similar among methods. Relationships were not detected between age or body weight and blood pressure. Significant differences in blood pressure were not detected between anxious and nonanxious dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Mean values of systolic, diastolic, and mean arterial blood pressure measured in nonsedated client-owned dogs, using invasive and noninvasive methods in a clinical setting, are comparable with those determined for acclimatized, trained, or sedated dogs. However, results of noninvasive methods may not accurately reflect direct values.

Epidemiological study of blood pressure in domestic cats

Blood pressure was measured indirectly in 203 cats using an oscillometric technique in conjunction with a tail cuff. Systolic blood pressure was found to be log normally distributed across the population, while diastolic pressure was log log normally distributed. Blood pressure was found to rise with age (systolic, diastolic, mean arterial and pulse pressure were significantly higher in animals aged 11 years or over than in animals aged under 11 years) but this rise did not parallel an increase in plasma urea or creatinine. Cats with clinical renal disease did however have higher blood pressures than normal cats, as did cats with ocular change consistent with hypertensive retinopathy.

Validation of impulse oscillometry in Friesian and Blue Belgian calves with respect to changes in extrathoracic upper airway resistance

Impulse oscillometry (IOS) was compared with conventional pulmonary function techniques (using oesophageal balloon and airflow measurements). Healthy Friesian (FR) and Blue Belgian (BB) calves were examined in different conditions of extrathoracic airway resistance (physiological and vertical head position). Higher resistance values were detected in BB calves compared with FR calves with both conventional and forced oscillation techniques in both head positions. Upper airway narrowing was characterised by increasing resistance values without changes in frequency dependence. Measuring input impedance in animals using a face mask, a considerable capacitive shunt of the upper airways (including the capacitive components of the mask) has to be taken into account. Even if the absolute value of this capacitive component is constant, its influence on the measurement results increases with growing frequency and with an increase in upper airway resistance. In conclusion, (1) impulse oscillometry is sensitive to upper airway resistance changes and (2) face mask capacitance is important and has frequency dependent effects on the respiratory impedance.

[Review of respiratory mechanics in animals. 3. Methodical and physiologic aspects of the use of the impulse oscilloresistometry system (OIS)]

The impulse oscillometry system (IOS) which was originally developed for human medicine was found to be suitable for analysing respiratory mechanics in spontaneously breathing animals. This technique is non-invasive.

METHODOLOGICAL ASPECTS

In order to use the IOS-technique in animals, a tightly fitting face mask is necessary. Furthermore, a flexible tube needs to be inserted into the measuring system. While the tube does not influence the measured results significantly, the face mask may affect the measurements. Therefore, its influence on the measured respiratory impedance must be taken into account. To prevent methodological errors, the head and body position of the animal should be standardised during the IOS-measurement. Since the methodological variability of the system is very small, the measuring results are highly reproducible. PHYSIOLOGICAL ASPECTS: In growing subjects, all parameters of respiratory mechanics depend on body weight. Since respiratory physiology is influenced by circadian rhythms, measurements of different days are only comparable when they have been done each day at the same hour. Comparing the respiratory impedance of different animals of similar age and body weight, a considerable inter-individual variability was observed. Due to the low level of physiological intra-individual variability, the method seems to be especially useful for studying influences on the respiratory system (i.e. pharmaceutics, therapeutics) in long-term studies using the same group of subjects.

[Review of respiratory mechanics in animals. 4. The diagnostic affirmation ability of research using the impulse oscilloresistometry system (IOS) in calves]

Taking methodological and physiological aspects into account (see Part 3), the impulse oscillometry system (IOS) was found to be sensitive to detecting and to quantifying clinically relevant changes in respiratory mechanics in calves. Therefore, the complex respiratory impedance needs to be measured in terms of resistance and reactance within the frequency range between 5 Hz and 20 Hz. The behaviour of resistance and reactance in dependence of frequency allows to differentiate and to localise airway obstructions. Obstructions of upper (extrathoracic) airways were mainly characterised by a frequency independent increase in the resistance. Within the reactance curve, no change in the resonant frequency could be observed. In a peripheral airway obstruction both resistance and reactance changed. The most typical finding concerning resistance was that a negative frequency dependence occurred. The reactance became more negative. Following this, the resonant frequency increased. With progressive obstruction of the peripheral airways, the reactance became more informative than resistance.

A comparison of indirect blood pressure monitoring techniques in the anesthetized cat

OBJECTIVE

To determine the accuracy of three indirect blood pressure monitoring techniques (oscillometric technique [OS], Doppler [DOP], and optical plethysmography [OP] [blood pressure determined with a pulse oximeter waveform]) when compared with direct arterial pressure measurement in cats.

STUDY DESIGN

Prospective study.

ANIMAL POPULATION

Eight healthy (five female, three male), domestic short-hair cats weighing 3.5 +/- 0.8 kg

METHODS

Cats were anesthetized with isoflurane. The inspired concentration of isoflurane was adjusted to produce mild hypotension (80 to 100 mm Hg direct systolic), moderate hypotension (60 to 80 mm Hg direct systolic), and severe hypotension (< 60 mm Hg direct systolic). Indirect pressure measurements were obtained from the thoracic limb and compared with concurrent direct measurement using regression analysis and a modification of Bland and Altman's technique.

RESULTS

All three techniques underestimated systolic pressure. OS produced the best prediction of systolic pressure with a bias +/- precision of -15.9 +/- 8.1 mm Hg. DOP and OP were relatively inaccurate with a bias +/- precision of -25 +/- 7.4 mm Hg and -25 +/- 7.5 mm Hg. All three techniques correlated well with direct pressure with r values of 0.81, 0.88, and 0.88 for OS, DOP, and OP. DOP and OP provided an accurate prediction of direct mean arterial pressure with a bias +/- precision of -0.8 +/- 6 mm Hg and 0.6 +/- 5.5 mm Hg. Correlation was good between DOP and mean arterial pressure with r = 0.89. Correlation was also good between OP and mean arterial pressure with r = 0.90.

CONCLUSIONS

OS provided the most accurate prediction of direct systolic pressure. DOP and OP provided a good prediction of mean arterial pressure in the cat.

CLINICAL RELEVANCE

All three of these techniques are useful for detecting trends. Direct monitoring of blood pressure should be considered if accurate blood pressure measurement is required.

Measurement of respiratory impedance in healthy calves using the impulse oscillation technique--physiological and methodological aspects

The aim of the present study was to investigate methodological and physiological aspects of complex respiratory impedance measurements in calves using the impulse oscillation technique. To apply the system to animals, a tightly fitting face mask was used. The measuring system was modified by placing a flexible tube between the pneumotachograph and the loudspeaker. Complex respiratory impedance measurements were not significantly influenced by the modification. Linear correlations were found between body weight and respiratory impedance; as body weight increased, resistance decreased and reactance increased. The methodological variability of impedance measurements using the impulse technique was found to be extremely small. Diurnal variations of respiratory impedance were considered to be the main source of intra-individual variability. When comparing different animals (even when healthy and matched for age and body weight) our results suggest that inter-individual biological variability must be carefully considered.

Longitudinal studies of reproducibility and variability of indirect (oscillometric) blood pressure measurements in dogs: evidence for tracking

To be clinically reliable, blood pressure readings taken in quiet surroundings with good technique from healthy, unstressed subjects accustomed to the procedure, should be reasonably constant between occasions. Apart from changes attributable to age or stress, sustained rises suggest hypertension. Yet it is increasingly realised that arterial pressure shows great short-term lability. Despite this, 'tracking' occurs in groups of humans, i.e. when ranked by blood pressure they tend to maintain their rank order. This paper examines month-on-month variability of arterial pressure, measured by non-invasive oscillometry (Dinamap) in both pet dogs and kennel populations. 'Tracking' occurred and there was also evidence of 'white coat' effects. Heart rate was more variable than arterial pressure and should not be used to reject pressure readings unless changes are extreme. There was further evidence that canine blood pressure rises with age.

Comparison of blood pressure measurements obtained in dogs by use of indirect oscillometry in a veterinary clinic versus at home

OBJECTIVE

To compare blood pressure and heart rate measurements performed in a veterinary clinic to similar measurements performed in a dog's home.

DESIGN

Prospective study.

ANIMALS

14 client-owned, clinically normal dogs.

PROCEDURE

Sequential blood pressure and heart rate measurements were recorded from the metatarsus and metacarpus of conscious dogs by indirect oscillometry. Measurements were performed in the dogs' homes and were repeated in a veterinary clinic. Blood pressures and heart rate were derived from 7 serial estimates over 8 to 10 minutes. Statistical differences between the home and clinic and between recording sites were calculated.

RESULTS

Systolic, diastolic, and mean blood pressure and heart rate measurements obtained from the metatarsus and metacarpus in the dogs' homes were significantly lower than measurements from the metatarsus in the clinic, but were similar to measurements from the metacarpus in the clinic. Significant differences were not found between blood pressure measurements from the metatarsus and metacarpus in the dogs' homes, but systolic and mean blood pressure and heart rate measurements from the metacarpus in the clinic were significantly lower than measurements from the metatarsus. Whereas all dogs had normal blood pressure in their homes, 5 of 14 dogs had transient hypertension (systolic pressure > 165 mm of Hg or diastolic pressure > 95 mm of Hg) in the clinic.

CLINICAL IMPLICATIONS

Blood pressure and heart rate measurements obtained in the clinic initially overestimate comparable measurements in a dog's home. The differences are best explained by transient autonomic responses to the stress of the clinic. Blood pressure must be measured by use of standardized techniques on dogs acclimated to the clinic environment.

Comparison of the indirect oscillometric and direct arterial methods for blood pressure measurements in anesthetized dogs

The indirect oscillometric method of blood pressure measurement was compared to the direct arterial puncture method in 15 anesthetized dogs, divided into three weight groups, undergoing a variety of surgical procedures. The objectives of this study were to determine the accuracy of the indirect oscillometric method at a single point in time and when sequential values were averaged. Additionally, the ability to detect systemic hypotension (i.e., mean systemic arterial pressure less than 60 mmHg) was evaluated. The method had the highest correlation coefficient (r of 0.8) when five sequential values were averaged and compared, and it appeared to be sensitive (100%) and specific (91%) for detecting hypotension.

Doppler ultrasonographic, oscillometric sphygmomanometric, and photoplethysmographic techniques for noninvasive blood pressure measurement in anesthetized cats

Blood pressure (BP) measurements obtained using 3 indirect BP measuring instruments, a Doppler ultrasonic flowmeter, an oscillometric device, and a photoplethysmograph, were compared with direct arterial pressure measurements in 11 anesthetized cats. The standard deviation of the differences (SDD) between direct and indirect pressure measurements were not significantly different from each other (P < .01), and ranged from 10.82 to 24.32 mm Hg. The high SDD values indicate that indirect BP estimates obtained with all these devices must be interpreted cautiously in individual patients. The mean errors (calculated as the sum of the differences between direct and indirect pressure measurements divided by the number of observations) of the 3 indirect devices were significantly different for systolic (SAP), diastolic (DAP), and mean (MAP) arterial pressures (P < .05). The Doppler and photoplethysmographic devices had the highest overall accuracy, as indicated by mean error values of less than 10 mm Hg. Correlation coefficients varied from .88 to .96 for the Doppler flowmeter, and from .85 to .94 for the photoplethysmograph; for both devices, the regression line slopes were close to unity. The Doppler flowmeter detected a pulse under all experimental conditions. The photoplethysmograph was also efficient in obtaining BP measurements, obtaining over 90% of SAP, DAP, and MAP readings attempted. The oscillometric device was the least accurate, with mean error values varying from 10 to 22 mm Hg. Correlation coefficients were high (.90 to .94) for this device, but the slopes of the regression lines were 0.7 to 0.8, indicating a trend for increased error at higher BP. The oscillometric device tended to underestimate BP by increasing amounts as the BP increased. The oscillometric device was the least efficient device for obtaining BP measurements (P < .01).