Studies on the Physiopathology of Chronic Obstructive Pulmonary Disease in the Horse. v. Blood Gas and Acid-base Valves during Exercise

LITTLEJOHN, A. & BOWLES, FELICITY, 198 1. Studies on the physiopathology of chronic obstructive pulmonary disease in the horse. V. Blood gas and acid-base values during exercise. Onderstepoort Journal of Veterinary Research, 48. 239-249 (I 981). The haemoglobin concentration, the partial pressures of oxygen a nd carbon dioxide, the oxygen content and the pH were determined in the arterial and mixed venous blood of 5 normal and 3 horses with chronic obstructive pulmonary disease (COPD) at 3 stages of a n exercise distance of 1200 m. Arteria l and mixed venous samples were col lected simultaneously by means of an automat ic technique during the wa lk, trot and gallop at 0100 m, at 500-600 m and at 1100-1 200 m. The standard bicarbonate and the lactic and pyruvic acid concentrations were also determined in arterial and mixed venous blood. Highly significant changes in the mean values of Pv02 , 0 2 conten t and 6 a-v 0 2 content occurred during exercise in COPD subjects, a nd significant changes in PvO, and 6 av 0 2 content occurred during exercise in norma l subjects. We concluded that COPD subjects compensated for respiratory dysfunction during exercise by extracting more oxygen from the blood than did normal horses. There was a highly significant correlation between the changes in standard bicarbonate and the changes in lactic acid concentration during exercise in both normal and COPD subjects. This Jed to the conclusion that lact ic acid production was primari ly, but not completely, responsible for the metabolic acidosis of exercise in horses. Resume ETUDES SUR LA PHYS!OPATHOLOG!E DE LA MALAD!£ D'OBSTRUCT!ON PULMONA JRE CHRONJQUE DU CHEVAL. V. GAZ DU SANG ET VA L EURS AC!DE-BASE PENDANT L 'EXERCICE La concentration d'haemog/obine, /es pressions partielles d'oxygime et de dioxyde de carbone. Ia teneur en oxygene et /e pH 0111 ete determines dans /e s(lng art erie/ et le sang veineux melange de cinq chevaux normaux et de trois chevaux atteints de Ia maladie d'obstruction pulmonaire chronique (COP D) a trois stades d'un exercice couvrant une distance de 1 200 m . Les echantillons arteriels et le sang veineux m elange ji.trent pris simu/tanement au moyen d'une technique automatique pendant Ia marche, /e trot et /e gallop a 0-100 m, a 500-600 met a I 1001 200m. Les concentrations standards de bicarbonate et d'acide lactique et pymvique furent ega/eme111 determinees dans /e sang arteriel et /e sang veineux m elange. Des changements significativement eleves dans /es valeurs moyennes de teneur PliO,, 0, et .6 ali 0 2 survinrent durant /'exercice des sujets COPD et des changements significati(s dans Ia teneur PliO, et 6 av02 survinrent pendant /'exercice des sujets normaux. Nous en avons deduit que les sujets COPD compensaient le manque respiratoire pendant /'exercice en pre/evant plus d'oxygene du sang que ne le faisaient /es chevaux normaux. II y eut une correlation hautement significative e111re les ch011f!ements dans Ia concentration standard du bicarbonate et d'acide lactique pendant /'exercice tant chez les sujets normaux que chez /es sujets COPD. Ceci conduisit a Ia conclusion que Ia production d'acide /actique hail principalement, mais non completement, responsab/e de /'acidose nl(!tabolique de /'exercice chez /es chevaux. I NTRODUCTION Bergsten (1974) determined the blood gas and acid-base values of 17 normal horses and 7 horses with chronic obstructive pulmonary di sease (COPD) while working on a treadmill at a velocity of 4 mjsec. Samples of a rterial and mixed venous blood were collected after 10 minutes exercise on the treadmill. In the normal subjects he noted signi ficant decreases in the partial pressure of carbon dioxide in arterial blood (PaC0 2) and in the partial pressure of oxygen in mixed venous blood (Pv0 2). In the COPD subjects there was a significant increase in the partial pressure of oxygen in arterial blood (Pa0 2) . When the blood gas values of the COPD subjects were compared with those of norma l subjects, Bergsten (I 974) found that the mean Pa0 2 of COPD subjects remained significantly lower than those of normal subjects and that the mean PvC0 2 (partial pressure of carbon dioxide in mixed venous blood) increased significantly in the COPD subjects with exercise, to a greater extent than in normal subjects. Received 23 September 1981 Editor 239 Arterial blood gases and pH were recorded in normal horses by Milne, Muir, Skarda, & Nicholl (1977) during tethered swimm ing. They found that the Pa0 2 decreased, the PaC0 2 increased and the arterial pH decreased during the tethered swimming exercise. Since there was no information regarding the effect of faster velocities or the effect of mass carried in the form of a rider, the foll owing studies were designed to investigate the effect of exercise at the walk. trot and gallop under the saddle o n the blood gas and acid-base values of normal horses and ho rses with COPD. It was considered that an analysi s of such effects would help to elucidate how horses with COPD compensate for lung dysfunction. MATERIALS AND METHODS Subjects Five clinically normal horses compnstng 2 Thoroughbreds, I Thoroughbred cross a nd 2 ponies were used as a control group. Subjects with COPD were I Thoroughbred cross and 2 ponies. The left carotid artery of each subject was translocated STUDIES ON THE PHYSIOPATHOLOGY OF CHRONIC OBSTRUCTIVE PULMONARY DISEASE IN THE HORSE. V. surgically to the subcutaneous position by the technique ofTavernor (1969). Collection of blood samples during exercise Simultaneous arterial and mixed venous blood samples were collected during exercise by means of the technique described by Littlejohn & Kruger (1976). Analysis of blood samples Blood gas partial pressures were determined by means of the techniques described in the preceding paper of this series (Littlejohn & Bowles, 1981). The oxygen content of blood samples collected during exercise was determined by the method of Van Slyke & Neill (1924) using a Van Slyke manometric gas apparatus* and following the technique published by the authors. The oxygen content of blood samples collected at rest was determined by calculation from the haemoglobin P02 and acid-base values, using the Severinghaus ( 1966) blood gas calculator to determine the percentage 0 2 saturations of the blood samples. The haemoglobin concentration of the blood samples was determined by the alkaline haematin method of Clegg & King (1942). Solution of the following equation provided oxygen content values in vols /;; : Hb (gm/100 mt) X 1, 33 X S0 2/;; 100 + ax lOO x P02 760 where 1 , 33 = oxygen content of 1 g of fully saturated haemoglobin S0 2 = percentage saturation of haemoglobin with oxygen a = solubility coefficient of oxygen at 38 oc and 760 mm Hg BP = 0,021 The value in vols % was then converted to t jt. The haematocrit values were determined by microcentrifugation . Excess lactate Lactic acid and pyruvic acid concentrations in blood samples were determined enzymatically using Sigmat reagents. The techniques followed were those described in Sigma Technical Bulletin No. 726-UV and No. 826-UV. A Bausch and Lomb Spectronic 70 spectrophotometer was used throughout. Values were determined by interpolation from calibration curves constructed for lactic and pyruvic acid with standard solutions. The excess lactate was calculated from the equation XL= (Ln-Lo)-(Pn-Po) (Lo/ Po) in which L and P denote lactate and pyruvate concentration in blood, and the postscripts n and o denote observed and control values respectively (Huckabee, 1958). Design of experiment Since the majority of horses involved in the racing industry in South Africa are trained and raced over distances of 8001 600 m, we considered that the most informative and relevant results would be gained by collecting samples at several stages of a work distance of 1200 m. * Baird & Tatlock, London t Sigma Chemical Co., Missouri 240 The track chosen was 600 m in length and oval in shape. Blood was collected from subjects at 3 stages during a 1 200m work distance, namely: 1. During the first 100m 2. Between 500 m and 600 m 3. Between 1 100m and 1 200m The oval shape of the track ensured that the subject could return to the saddling enclosure immediately after the samples had been collected. There was therefore a time lag of only 2 min. at most between the collection of the samples and their analysis, or the preparation of aliquots for analysis as in the case of lactic and pyruvic acid, Subjects were ridden daily for 3 weeks prior to the experiment so that each subject was in a similar state of physical ability. The blood collections were done as follows: Each day subjects were ridden at walk, trot and canter for I 200 m at each pace. Cannulae were placed in situ in the carotid artery and right ventricle the day before the first collection. On the first sampling day, samples were collected during the first 100 m of the walk, the trot and the canter, by instructing the rider to release the spring-loaded plungers at the moment horse and rider set off. On the second day samples were collected during the 500 m600 m period by instructing the rider to release the mechanism at the moment of passing the 500 m mark. On the third day, samples were collected during the 1 100-1 200 m period by instructing the rider to release t!':e mechanism at the moment of passing the 1 100m mark. The horse and rider returned immediately to the saddling enclosure as soon as the I 00 m, 600 m or I 200 m marks had been passed. On days when 100 m or 600 m samples were collected, the I 200 m circuit at each pace was completed so that subjects received the same work period every day. The speed of horse and rider was measured over a distance of 50 m during each occasion when blood was collected to ensure that work loads for both normal and COPD horses, although not identical, were comparable. Statistical analyses of results The standard error of the difference (Sd) formula for determining the "t" values of paired observations was as follows: Sd (.E individual differences) • . . ••• • • •• . • ••• •. n(n1) .E (individual differences)2 n n(n-1) For unpaired observations 2 2 Sd= n1SD1 + n2SD2 n1 + n22 The level of probability accepted as significant was P<O,Ol. RESULTS The mean values and standard deviations of each determination obtained from the 2 groups of subject£ at the 0100 m, 500600 m and 1 I 001 200 m stages of the work periods at walk, trot and gallop are plotted in Fig. 18. A. LITTLEJOHN & FELICITY BOWLES TABLE 1 Significant changes from control values of blood determinations in normal and COPD subjects at the 0-100 m, 500-600 m and 1100-1200 m stages of work distances at walk, trot and gallop Normal COPD Exercise 0-100 m 500-600 m 11100-1200 m 0-100 m 500-600 m 11 100-1200 m Ht. .. .. . .. . . .. . .. . . Walk .... ....... . v Trot. . . ... . .. .... v Gallop ..... ... . . v 1 f t t t Hb ... . .. .. ... . .... . Walk .. . .. ... . . . . v f t Trot .. . . .... ... . . v Gallop . ... .. . ... v t i t t ----P02 •••••.• • ...••• •• Walk .. . ........ . ~ ** * Trot . .. ..... . .... ~ ** ** I ! I ! ! ! Gallop ... . ...... ~ ! I * ** ! ! I ! ! I ! I I I -----------0 2 content . .. ...... . Walk ........ a v t t i I ! * Trot. . ... ... . .... a v i t J I I I Gallop .. .. . .... . ~ I J ! t I -------------(av) o. content ... . . Walk .. ... . . .... . Trot. ..... . . . ... . Gallop ..... . ... . i t t i t i i i ** 1 i I I + i I ------·--------------reo •..... . .. . ..... Walk ............ a v i i Trot . ...... . ..... a v Gallop .......... ~ J I I I I ! I * i i -----_____ ,. ---------pH . .. ... .. ... . ... . . Walk ............ ~ Trot.. ... .... . . ~ Gallop ...... . .. . ~ -----------------------·----1---------------Standard bicorbonate Walk . .. . . ... . ... a Trot ......... . ... a Gallop .... ... .... a ---·-----------------------Excess lactate..... . . . Walk ............ a Legend: a v Trot. ... . .. .. .... a Gallop .... .. .... a = arterial = mixed venous f i t t t i i t i t t i l i t or I = Mean value different from control value at P < 0 ,05 I 1 = Mean value significantly different from control value at P< O,Ol I 1 I = Mean value significantly different from control value at P< O,OOl i i or i i i or * ** = Mean value different from corresponding mean value of normal subjects (P < O, 05) ~= Mean value significantly different from corresponding mean value of normal subjects (P< O,Ol) Significant changes from control resting values of each group are given in Table 1 in addition to significant differences between corresponding mean values of each group. Changes in individual parameters are discussed below. The mean speeds at walk, trot and gallop and standard deviations in mjsec. for 5 normal and 3 COPD subjects were as follows: Walk; normal= I ,58 ± 0 , 32, COPD = 1,51 ± 0, 10 Trot; normal= 3, 73 ± 0,69, COPD = 4, 19± 0,64 Gallop; normal= 7, 74± 1, 12, COPD = 7 ,59± 1 ,86 The above figures were calculated from the speed measured at the time of blood collection. There were no significant differences between the mean values of normal and COPD subjects at corresponding paces. 241 DISCUSSION Haematocrit and haemoglobin The large increases in haematocrit and haemoglobin which occur in horses subjected to stressful stimuli have been well documented ; thus they increase during excercise (Persson, 1967; Bergsten, 1974; Von Engelhardt, 1977), excitement (Torten & Scha1m, 1964; Stewart & Steel, 1974), casting (Littlejohn, 1969), swimming (Fregin & Nicholl, 1977) and after injection of adrenalin (lrvine, 1958; Persson, 1967). Persson (1967) showed that the venous haematocrit of horses trotting on a treadmill increased from 36-44% to 4652% during trotting exercise on a treadmill at 5 mjsec. In the present study, the mean mixed venous haemoglobin concentration of normal STUDIES ON THE PHYSIOPATHOLOGY OF CHRONIC OBSTRUCTIVE PULMONARY DISEASE IN THE HORSE. Y.