There are a range of biological pressures of interest to researchers, such as arterial pressure, ventricular pressure, intracranial pressure, venous pressure, thoracic pressure, bladder pressure etc. Each application has a different requirement for the pressure sensor. For example, left ventricular pressure requires a high sampling frequency and frequency response while intracranial pressure requires accuracy at low pressure values.
The Millar Rat Telemetry utilizes a solid state pressure sensor to provide high fidelity recordings with sensitivity for performance at both high and low pressure values.
The left ventricle provides the pressure required to circulate blood in the systemic circulation and perfuse tissues and organs. The pressure is generated from the contraction of the muscle wall of the left ventricle and thus, peak left ventricular pressure is similar in value to peak systolic pressure. As there are two phases in the cardiac cycle, systole and diastole, the contraction and relaxation of the ventricle generates cyclic pressure waveforms with a large amplitude.
With a high fidelity pressure sensor, one can more accurately record the rapid changes in pressure which occur as the ventricle contracts, i.e.: as the maximum rate of change in pressure (dP/dt). Solid state pressure sensors are advantageous over the legacy gel filled catheter tips because their fast frequency responses. The measurement of left ventricular pressures also requires a pressure sensor with a large range in sensitivity to accurately capture low pressure values such as the left ventricular pressure during diastole.
Chronic measurement of LVP and dP/dt allows tracking of disease progression, such as heart failure in myocardial infarct models, or the effects of drug-induced changes. Thus, the chronic measurement of LVP can be useful for studies in basic cardiovascular physiology, as well as pharmaceutical drug development.
An example of simultaneous arterial pressure, left ventricular pressure and the dP/dt calculation from a rat recorded using the Millar TRM54PP telemeter is shown below.
Arterial pressure is generated by the contraction of the heart and maintained during diastole by the elastance of the aorta and the resistance of the vasculature allowing for continuous perfusion of tissues and organs.
Arterial pressure can be measured in the abdominal aorta, the femoral artery and the carotid artery. Lower pulse pressure values (difference between systolic and diastolic pressures) and different waveform shapes will be measured at sites further away from the heart, e.g. in the femoral artery compared to the abdominal aorta. From the arterial pressure profile, one can also study the circadian and estrous rhythms (female rats). Variables that can be measured or calculated from the arterial pressure waveform include:
The chronic measurement of arterial pressure via telemetry can be useful for many areas in medical science from basic cardiovascular science to safety pharmacology and toxicity studies.
An example of the arterial pressure waveform from the Millar TRM54P telemeter implanted in the abdominal aorta is shown below.
Millar telemeters are also sensitive enough to allow for high-resolution measurement of low pressure values. Low pressure biological signals include left ventricular pressure during diastole, intracranial pressure, venous pressure and bladder pressure.
Intracranial pressure is the pressure inside the skull (and within the brain tissue) and can be altered by the production and drainage of cerebrospinal fluid. In humans, intracranial pressure can increase in individuals with hydrocephalus or those who have had traumatic brain injury. The measurement of ICP in rats can be good models for the study of emergency and trauma medicine, and in neuroscience and behavioral studies. The chronic measurement of ICP in addition to arterial pressure can also provide information on the central perfusion pressures.
Measurement of dual pressure recordings, as well as pressure and biopotential is also possible. The combination of pressure recordings with biopotential recordings can provide valuable data to study temporal relationships between two variables. Examples of useful combinations using the TRM54PP or the TRM54PB include the following:
|Arterial pressure + LVP||Arterial pressure + ECG|
|Arterial pressure + ICP||LVP + ECG|
|ICP + EEG|
|ICP + Nuchal EMG|
Millar cohousing also enables the recording of pressure with other biological signals such as oxygen telemetry. Simultaneous recordings of arterial pressure (TRM54P) and renal oxygen concentrations (TR57Y), or arterial pressure + sympathetic nerve activity (TRM56SP) and renal oxygen concentrations (TR57Y) may prove to be valuable in cardiovascular control studies.