Normal Respiratory Values
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Conversion Table for Common Values | ||
Data | SI Units* | Other Units |
Pressure | 1 kPa | 7.5 mmHg |
| 1 kPa | 10.2 cmH2O |
| 1 kPa | 10 mbar |
| 1 kPa | 0.0099 atm |
| 1 kPa | 0.1 N/cm2 |
Work | 1 J | 0.239 cal |
| 1 J | 10.2 cmH2O.cm2 |
Power | 1 W | 0.0143 kcal/min |
Gas exchange | 1 mmol/min | 22.4 ml/min |
Gas content | 1 mmol/liter | 2.24 ml/dl |
Hemoglobin | 1 mmol/liter | 16.1 g/liter |
*SI Units = International System of Units. | ||
1. Normal Ventilation Values
1.1. Normal Ventilation Values in Adult Horses
Mean ventilation values in healthy Thoroughbred horses are considered average for their quality, fitness, age (5 years), and size (mean body weight 470 kg) and running on a treadmill under temperature climatic conditions (lung and gas volumes are expressed as BTPS and STPD respectively). Measurements were made at 6 m/s at walk (duration: 5 minutes), 3.4 m/s at trot (duration: 5 minutes), 8 m/s at canter (duration: 1 minute) and 10 m/s with 4% slope incline at gallop (duration: 1 minute) and 5 minutes after recovery [1].
Value | Unit | Rest | Walk | Slow Trot | Canter | Fast Gallop | Recovery |
VO2max% | % | 3.3 | 14 | 18 | 60 | 100 | 20 |
VT | liters | 5.6 | 5.8 | 6.2 | 9.2 | 13.2 | 6.5 |
VD | liters | 3.4 | 3.4 | 3.5 | 2.6 | 2.6 | 3.5 |
VA | liters | 2.2 | 2.4 | 2.8 | 6.6 | 10.6 | 3.0 |
VD/VT | % | 60 | 58 | 57 | 28 | 20 | 54 |
f | breaths/min | 14 | 65 | 91 | 113 | 121 | 110 |
ti | seconds | 1.9 | 0.45 | 0.34 | 0.27 | 0.25 | 0.29 |
te | seconds | 2.4 | 0.47 | 0.32 | 0.27 | 0.25 | 0.26 |
ti/ttot | % | 44 | 49 | 52 | 50 | 50 | 53 |
E | liters/min | 78 | 377 | 564 | 1040 | 1598 | 715 |
D | liters/min | 47 | 219 | 321 | 291 | 320 | 386 |
A | liters/min | 31 | 158 | 243 | 749 | 1278 | 329 |
E/VO2 | liters/liter | 35 | 40 | 47 | 26 | 24 | 55 |
E/VCO2 | liters/liter | 43 | 48 | 51 | 27 | 23 | 51 |
mean i | liters/s | 2.9 | 13 | 19 | 34 | 53 | 26 |
mean e | liters/s | 2.3 | 12 | 20 | 34 | 53 | 30 |
imax | liters/s | 4.1 | 14 | 27 | 45 | 64 | 32 |
emax | liters/s | 4.2 | 18 | 30 | 52 | 79 | 39 |
i | liters/s2 | 8 | 240 | 632 | 1124 | 1685 | 650 |
e | liters/s2 | 7 | 225 | 566 | 1086 | 1595 | 744 |
VO2max %: percent of maximal oxygen uptake; VT: tidal volume; VD: physiological dead space; VA: alveolar volume; VD/VT: ratio of dead space to tidal volume; f: breathing frequency; ti: inspiratory time of the breathing cycle; te: expiratory time; ti/ttot: ratio of inspiratory to total time of the breathing cycle; E: minute volume; D: dead space ventilation; A: alveolar ventilation; E/VO2: ventilatory equivalent for oxygen uptake; E/VCO2: ventilatory equivalent for carbon dioxide output; mean i: mean inspiratory flow or inspiratory drive; mean e: mean expiratory flow; imax: peak inspiratory flow; emax: peak expiratory flow; i: volume acceleration at the onset of inspiration; e: volume acceleration at the onset of expiration. | |||||||
1.2. Normal Ventilation in Neonate Foals
Ventilatory parameters and pressure changes during normal tidal breathing in the standing foal less than 1 week of age [2,3] | ||||||||
Age in Days | n | VT (L) | VT/kg (ml/kg) | f (bpm) | E(L/min) | E/kg (ml/kg) | Ti (sec) | Te (sec) |
2 | 7 | 0.65 ± 0.15 | 15.8 ± 2.5 | 53.9 ± 9.9 | 34.8 ± 12.0 | 848 ± 231 | 0.51 ± 0.15 | 0.72 ± 0.09 |
7 | 9 | 0.90 ± 0.17 | 17.6 ±3.0 | 40.9 ± 5.2 | 33.9 ± 7.5 | 717 ± 157 | 0.65 ± 0.10 | 0.75 ± 0.17 |
Values are means ± s.d. VT: tidal volume; f: frequency of breathing, bpm: breaths per minute; E: minute ventilation; Ti: inspiratory time; Te: expiratory time. | ||||||||
2. Normal Values of Breathing Mechanics
2.1. Normal Values of Breathing Mechanics in Adult Horses
Mean ventilation values in healthy Thoroughbred horses are considered average for their quality, fitness, age (5 years), and size (mean body weight 470 kg) and running on a treadmill under temperature climatic conditions (lung and gas volumes are expressed as BTPS and STPD respectively). Measurements were made at 6 m/s at walk (duration: 5 minutes), 3.4 m/s at trot (duration: 5 minutes), 8 m/s at canter (duration: 1 minute) and 10 m/s with 4% slope incline at gallop (duration: 1 minute) and 5 minutes after recovery [1].
Value | Unit | Rest | Walk | Slow Trot | Canter | Fast Gallop | Recover 5' |
Ppl min | kPa | -0.78 | -1.19 | -1.78 | -3.19 | -4.85 | -1.68 |
Ppl max | kPa | -0.34 | 0.31 | 0.55 | 2.42 | 3.62 | 0.53 |
MaxΔPpl | kPa | 0.44 | 1.50 | 2.33 | 5.61 | 8.47 | 2.21 |
Pin | kPa | 0.02 | 0.54 | 1.16 | 2.61 | 4.26 | 1.71 |
ΔPV = 0 | kPa | 0.24 | -0.29 | -0.90 | -2.42 | -3.88 | -1.90 |
Cdyn | liter/kPa | 23 | -20 | -6.8 | -3.8 | -3.4 | -3.4 |
RL | Pa/liter/s | 25 | 26 | 30 | 48 | 57 | 27 |
RUA | Pa/liter/s | 20 | 21 | 23 | 38 | 46 | 21 |
RLA | Pa/liter/s | 5 | 5 | 7 | 10 | 11 | 6 |
Wvis | J | 1.4 | 6.2 | 14 | 36 | 82 | 14 |
vis | J/min | 17 | 403 | 1274 | 4068 | 9922 | 1540 |
vis/VE | J/min | 0.22 | 1.07 | 2.2 | 3.9 | 6.2 | 2.2 |
vis/VO2 | J/liter | 7.7 | 42 | 106 | 102 | 148 | 118 |
Ppl min: peak intrapleural pressure recorded during inspiration; Ppl max: peak intrapleural pressure recorded during expiration; maxΔPpl: maximum change in intrapleural pressure; Pin: initial pressure; ΔPV=0: intrapleural pressure gradient between the 2 points of zero flow; Cdyn: dynamic lung compliance; RL: total pulmonary resistance; RUA: upper airways resistance; RLA: lower airways resistance; vis: viscous work of breathing; vis: minute work of breathing; vis/VE: work of breathing per ventilated liter; vis/VO2: work of breathing per liter of oxygen uptake. | |||||||
2.2. Normal Values of Impulse Oscillometry Mechanics in Adult Horses
Values of respiratory resistance (Rrs) measured from 5 to 35 Hz with the Impulse Oscillometry System (IOS) [4] | ||||
Rrs (kPa/l/s) | Mean | SD | CLL | CLU |
R5Hz | 0.070 | 0.012 | 0.066 | 0.074 |
R10Hz | 0.081 | 0.011 | 0.077 | 0.085 |
R15Hz | 0.088 | 0.012 | 0.085 | 0.092 |
R20Hz | 0.079 | 0.010 | 0.076 | 0.083 |
R25Hz | 0.075 | 0.010 | 0.072 | 0.078 |
R35Hz | 0.062 | 0.009 | 0.059 | 0.065 |
SD: Standard deviation, CLL: 95% lower confidence limit, CLU: 95% upper confidence limit | ||||
Values of reactance (Xrs) measured from 5 to 35 Hz with the Impulse Oscillometry System (IOS) [4] | ||||
Xrs (kPa/l/s) | Mean | SD | CLL | CLU |
X5Hz | 0.020 | 0.007 | 0.017 | 0.022 |
X10Hz | 0.015 | 0.009 | 0.012 | 0.018 |
X15Hz | 0.009 | 0.012 | 0.005 | 0.013 |
X20Hz | 0.006 | 0.015 | 0.001 | 0.010 |
X25Hz | 0.003 | 0.013 | -0.001 | 0.008 |
X35Hz | -0.003 | 0.010 | -0.007 | 0.000 |
SD: Standard deviation, CLL: 95% lower confidence limit, CLU: 95% upper confidence limit | ||||
3. Normal Gas Exchange Values
3.1. Normal Values of Blood Gases in Adult Horses
PaO2 85 - 105 mmHg
PaCO2 42 - 46 mmHg
pH 7.38 - 7.42
Mean ventilation values in healthy Thoroughbred horses are considered average for their quality, fitness, age (5 years), and size (mean body weight 470 kg) and running on a treadmill under temperature climatic conditions (lung and gas volumes are expressed as BTPS and STPD respectively). Measurements were made at 6 m/s at walk (duration: 5 minutes), 3.4 m/s at trot (duration: 5 minutes), 8 m/s at canter (duration: 1 minute) and 10 m/s with 4% slope incline at gallop (duration: 1 minute) and 5 minutes after recovery [1].
Value | Unit | Rest | Walk | Slow Trot | Canter | Fast Gallop | Recover 5' |
O2 | ml/kg/min | 4.7 | 20.2 | 25.5 | 85.1 | 142.5 | 27.7 |
CO2 | ml/kg/min | 3.8 | 17.0 | 23.4 | 80.9 | 146.8 | 29.8 |
R | - | 0.82 | 0.85 | 0.92 | 0.95 | 1.03 | 1.07 |
Venous PO2 | mmHg | 39 | 32 | 30 | 25 | 16 | 62 |
Venous PCO2 | mmHg | 47 | 49 | 50 | 64 | 96 | 43 |
HCO3- | mmol/liter | 28.8 | 28.9 | 27.5 | 26.6 | 23.0 | 19.2 |
Arterial PO2 | mmHg | 95 | 101 | 99 | 83 | 69 | 115 |
Arterial PCO2 | mmHg | 45 | 44 | 43 | 46 | 50 | 32 |
(A-a) ΔO2 | mmHg | 4 | 2 | 4 | 16 | 29 | 6 |
pHa | - | 7.39 | 7.40 | 7.40 | 7.39 | 7.26 | 7.36 |
PCV | % | 38 | 42 | 44 | 48 | 58 | 56 |
Hb | G/liter | 140 | 150 | 160 | 175 | 220 | 220 |
Arterial SO2 | % | 97 | 97.5 | 97 | 95 | 90 | 98.5 |
Arterial CO2 | liter% | 20 | 22 | 22 | 25 | 28 | 33 |
Venous CO2 | liter% | 14 | 11 | 11 | 7 | 5 | 21 |
C(a-v)O2 | liter% | 6 | 11 | 11 | 18 | 23 | 12 |
Alveolar PO2 | mmHg | 99 | 103 | 103 | 99 | 98 | 121 |
Alveolar PCO2 | mmHg | 44 | 43 | 42 | 45 | 49 | 31 |
FmeO2 | % | 16.2 | 17.0 | 17.7 | 14.9 | 14.3 | 18.4 |
FmeCO2 | % | 2.6 | 2.6 | 2.5 | 4.6 | 5.4 | 2.1 |
FetO2 | % | 14.0 | 14.5 | 14.5 | 13.9 | 13.9 | 17.2 |
FetCO2 | % | 6.3 | 6.1 | 6.0 | 6.4 | 7.0 | 4.5 |
O2: oxygen uptake; CO2: carbon dioxide output; R: respiratory exchange ratio; venous PO2: venous oxygen partial pressure; venous PCO2: venous carbon dioxide partial pressure; arterial PO2: arterial oxygen partial pressure; arterial PCO2: arterial carbon dioxide partial pressure; HCO3-: bicarbonate content; [A-a] ΔO2: alveolar-arterial oxygen gradient; pHa: arterial pH; PCV: packed cell volume; Hb: blood hemoglobin concentration; arterial SO2: percent saturation of hemoglobin with oxygen; arterial CO2: arterial oxygen content; venous CO2: venous oxygen content; C(a-v)O2: arteriovenous oxygen content gradient; alveolar PO2: alveolar oxygen partial pressure; alveolar PCO2: alveolar carbon dioxide partial pressure; FmeO2: mixed expired oxygen fraction; FmeCO2: mixed expired carbon dioxide fraction; FetO2: end-tidal oxygen fraction; FetCO2: end-tidal carbon dioxide fraction. | |||||||
3.2. Normal Values of Arterial Blood Gases in Foals
Values measured from birth until 1 week (expressed as mean ± SEM) | ||||||||
Gestational Age/Status | Postnatal Age | Position | pH | PaCO2 mmHg | PaO2 mmHg | HCO3 | n | Ref |
Normal | 3 - 168 hr | Lateral | 7.354 ± 0.011 | 47.5 ± 2.6 | 80.0 ± 3.8 |
| 10 | [5] |
Normal | 1 - 12 hr 12 - 48 hr 48 - 168 hr | Lateral | 7.378 ± 0.015 3.374 ± 0.004 7.384 ± 0.014 | 42.2 ± 1.8 44.5 ± 1.2 42.4 ± 1.0 | 77.3 ± 3.1 83.2 ± 3.1 88.2 ± 5.9 |
| 6 6 5 | [6] |
Normal | 4 - 11 hr | Lateral | 7.367 ± 0.10 | 39.5 ± 1.8 | 83.8 ± 6.3 |
| 5 | [7] |
Normal | 24 hr 24 hr 48 hr 48 hr 72 hr 72 hr 144 hr 144 hr | Standing Lateral Standing Lateral Standing Lateral Standing Lateral | 7.41 ± 0.03 7.38 ± 0.05 7.40 ± 0.03 7.37 ± 0.00 7.39 ± 0.07 7.44 ± 0.14 7.42 ± 0.03 7.41 ± 0.03 | 45.2 ± 2.5 48.1 ± 3.8 47.5 ± 3.7 49.5 ± 2.8 49.6 ± 1.5 51.6 ± 7.2 47.3 ± 2.3 46.9 ± 2.1 | 84.6 ± 6.9 72.69 ± 14.2 106.6 ± 3.9 89.6 ± 12.7 104.5 ± 4.8 94.1 ± 4.3 98.8 ± 4.8 84.2 ± 6.9 |
| 3 3 3 3 5 5 5 5 | [8] |
Premature | 0.5 - 11 hr | Lateral | 7.208 ± 0.48 | 55.3 ± 3.6 | 53.7 ± 1.5 |
| 7 | [6] |
Term | Birth 2 min 15 min 30 min 60 min 2 hr 4 hr 12 hr 24 hr 48 hr 96 hr | Lateral Lateral Lateral Lateral Lateral Lateral Lateral Lateral Lateral Lateral Lateral | 7.413 ± 0.019 7.312 ± 0.016 7.322 ± 0.025 7.354 ± 0.010 7.362 ± 0.013 7.362 ± 0.012 7.355 ± 0.017 7.357 ± 0.024 7.393 ± 0.012 7.398 ± 0.008 7.396 ± 0.012 | 45.7 ± 1.1 54.1 ± 2.0 50.4 ± 2.7 51.5 ± 1.5 47.3 ± 2.2 47.7 ± 1.7 45.0 ± 1.9 44.3 ± 1.2 45.5 ± 1.5 46.1 ± 1.1 45.8 ± 1.1 | 39.7 ± 2.1 56.4 ± 2.3 57.5 ± 3.6 57.0 ± 1.8 60.9 ± 2.7 66.5 ± 2.3 75.7 ± 4.9 73.5 ± 3.0 67.6 ± 4.4 74.9 ± 3.3 81.2 ± 3.1 | 26.3 ± 1.1 24.0 ± 1.2 24.4 ± 1.6 25.3 ± 0.7 25.3 ± 1.0 25.0 ± 0.9 23.6 ± 1.1 23.2 ± 1.3 26.2 ± 1.1 25.7 ± 0.6 23.2 ± 2.1 | 8 10 9 10 9 8 10 10 9 8 8 | [9] |
4. Pulmonary Hemodynamics
Mean ventilation values in healthy Thoroughbred horses are considered average for their quality, fitness, age (5 years), and size (mean body weight 470 kg) and running on a treadmill under temperature climatic conditions (lung and gas volumes are expressed as BTPS and STPD respectively). Measurements were made at 6 m/s at walk (duration: 5 minutes), 3.4 m/s at trot (duration: 5 minutes), 8 m/s at canter (duration: 1 minute) and 10 m/s with 4% slope incline at gallop (duration: 1 minute) and 5 minutes after recovery [1].
Value | Unit | Rest | Walk | Slow Trot | Canter | Fast Gallop | Recover 5' |
HR | beats/min | 35 | 75 | 103 | 155 | 210 | 83 |
SV | liters | 1.05 | 1.07 | 1.12 | 1.39 | 1.36 | 1.32 |
Q | liters/min | 37 | 80 | 115 | 215 | 285 | 110 |
PaPmax | mmHg | 37 | 69 | 78 | 99 | 152 | 53 |
PaPmin | mmHg | 22 | 30 | 39 | 47 | 50 | 26 |
PaPm | mmHg | 28 | 43 | 52 | 65 | 82 | 35 |
Pw | mmHg | 16 | 25 | 30 | 37 | 49 | 20 |
P (aP-w) | mmHg | 12 | 18 | 22 | 28 | 33 | 15 |
PVR | mmHg/liter/min | 0.32 | 0.22 | 0.19 | 0.13 | 0.11 | 0.14 |
T°a | °C | 37.5 | 37.9 | 38.1 | 38.7 | 41.3 | 39.7 |
O2/HR | ml/kg/beat | 0.06 | 0.25 | 0.25 | 0.55 | 0.68 | 0.34 |
A/Q | liters/liter | 0.84 | 1.98 | 2.11 | 3.48 | 4.48 | 3.00 |
HR: heart rate; SV: stroke volume; Q: cardiac output; PaPmax: maximal pulmonary artery pressure; PaPmin: minimal pulmonary artery pressure; PaPm: mean pulmonary artery pressure; Pw: pulmonary artery wedge pressure; P(aP-w): pulmonary driving pressure; PVR: pulmonary vascular resistance; T°a: arterial blood temperature; O2/HR: oxygen pulse; A/Q: global ventilation/perfusion ratio. | |||||||
1. Lekeux P, Art T. The respiratory system: anatomy, physiology, and adaptations to exercise and training. In: Hodgson DR, Rose RJ. Eds. The athletic horse: principles and practice of equine sports medicine. Philadelphia: WB Saunders Company, 1994, pp 79-127. - Available from amazon.com -
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Affiliation of the authors at the time of publication
Department of Physiology and Sport Medicine, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium.
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