Age-related differences in blood pressure, ultrasound-derived arterial diameters and arterial wall stiffness parameters in horses

Spectral Doppler of aortic and carotid blood flow in horses with aortic valve regurgitation

OBJECTIVES

This study aimed to compare two-dimensional, M-mode, color, pulsed-wave Doppler (PWD) and continuous-wave Doppler (CWD) echocardiography, and PWD ultrasonography of the caudal common carotid artery (CCA) in horses with aortic regurgitation (AR).

ANIMALS

Warmblood horses without (n = 20) and with mild, moderate, and severe AR (n = 60) were included in the study.

MATERIALS AND METHODS

A retrospective descriptive study focused on cardiac dimensions, aortic and CCA Doppler flow. Non-invasive blood pressure and presence of ventricular arrhythmia were recorded. Groups were compared using analysis of variance, chi-square, Spearman's rho, and Kruskal-Wallis tests.

RESULTS

Maximal aortic antegrade flow velocity was higher in horses with moderate and severe AR than in normal horses and higher in those with severe AR than in those with mild AR (P<0.001). Mean (standard deviation) antegrade CCA flow velocities were 0.9 m/s (0.3 m/s) in normal horses and 1.0 m/s (0.2 m/s), 1.2 m/s (0.3 m/s), and 1.5 m/s (0.4 m/s) in horses with mild, moderate, and severe AR, respectively. Retrograde mid-to-end diastolic PWD ultrasonography of the common carotid artery (PWD-CCA) flow occurred in horses with moderate (6/20) and severe (13/20) AR. The presence of pathologic retrograde PWD-CCA flow was associated with presence of increased left ventricular dimensions and pulse pressures >60 mmHg. The CWD regurgitant jet pressure half-time failed to differentiate between AR severity grades.

STUDY LIMITATIONS

The limitations of this study included retrospective design with missing values, AR classification system not validated by longitudinal follow-up, and CCA retrograde velocities <10 cm/s not measured.

CONCLUSIONS

Pulsed-wave Doppler ultrasonography of the common carotid artery identifies moderate and severe AR in horses with hemodynamic overload. Presence of retrograde PWD-CCA flow was associated with moderate and severe AR and with left ventricular dilation. Quantification of CWD pressure half-time appeared unreliable for AR severity assessment.

Effect of physiological and pharmacological stress on heart rate, blood pressure, and echocardiographic measurements in healthy Warmblood horses

BACKGROUND

Echocardiographic measurements are important prognostic indicators but might be influenced by heart rate and blood pressure. This is particularly important when comparing repeated examinations.

HYPOTHESIS

To determine the effect of physiological stress at mildly increased heart rates and pharmacological challenge using IV administration of N-butylscopolammonium bromide and metamizol sodium on heart rate, blood pressure, and echocardiographic measurements.

ANIMALS

Twenty healthy Warmblood horses.

METHODS

Randomized crossover study. Horses were examined echocardiographically by 2-dimensional, M-mode, pulsed wave (PW) Doppler, and PW tissue Doppler imaging with simultaneous ECG recording and noninvasive blood pressure measurements during rest, physiological stress, and pharmacological challenge. Cardiac dimensions and functions were measured by a blinded observer. Data were analyzed using repeated-measures analysis of variance.

RESULTS

Mean heart rate and arterial blood pressure were significantly higher during physiological stress (46 ± 2 bpm, 93 ± 16 mm Hg) and pharmacological challenge (62 ± 13 bpm, 107 ± 17 mm Hg) compared with rest (34 ± 3 bpm, 86 ± 12 mm Hg; P < .05). Compared with rest, physiological stress resulted in increased left atrial fractional area change (34.3 ± 7.5 vs 27.3 ± 5.1%; P = .01) and left ventricular late diastolic radial wall motion velocity (13 ± 3 vs 10 ± 2 cm/s; P = .01) but had no significant effect on most other echocardiographic variables. Compared with rest, pharmacological challenge led to significantly decreased left atrial and diastolic ventricular dimensions (left ventricular internal diameter: 10.3 ± 0.9 vs 10.7 ± 0.8 cm; P = .01), increased aortic and pulmonary diameters, and ventricular wall thickness.

CONCLUSIONS AND CLINICAL IMPORTANCE

Physiological stress at mildly increased heart rates significantly enhanced atrial pump function. Larger heart rate and blood pressure increases during pharmacological challenge resulted in altered cardiac dimensions. This should be taken into account when evaluating echocardiographic measurements at increased heart rates.

Histological and biomechanical properties of systemic arteries in young and old Warmblood horses

Arterial rupture is a well-recognized cause of sudden death in horses, which mainly affects older horses. The arterial wall is known to stiffen with age, although the underlying age-related histological and biomechanical changes remain unclear. The purpose of this study was to investigate the effect of aging by histological analysis of the arterial wall and examination of the arterial wall biomechanical properties using an inflation-extension test. Entire circular samples of the proximal and distal aorta, cranial and caudal common carotid, external iliac, femoral and median artery were collected from 6 young (6 years) and 14 old horses (≥15 years). Samples of all arteries were histologically examined and intima media thickness as well as area % of elastin, smooth muscle actin and collagen type I and III were determined. Older horses had a significantly larger intima media thickness and a significantly higher area % of smooth muscle actin compared to young horses. Samples of the proximal and distal aorta, the caudal common carotid and the external iliac artery were mechanically assessed using an in-house developed inflation-extension device with ultrasound analysis. Rupture occurred in a minority of arteries (8/78) at high pressures (between 250-300 mmHg), and mostly occurred in older horses (7/8). Pressure-area, pressure-compliance and pressure-distensibility curves were constructed. A significant difference in the pressure-area curves of the distal aorta, common carotid artery and external iliac artery, the pressure-compliance curves of the proximal aorta and carotid artery and the pressure-distensibility curve of the proximal aorta was observed between young and old horses. Results demonstrate an effect of age on the histological and biomechanical properties of the arterial wall, which might explain why arterial rupture occurs more often in older horses.