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Guild S.-J.,University of Auckland | Barrett C.J.,University of Auckland | McBryde F.D.,University of Auckland | Van Vliet B.N.,Memorial University of Newfoundland | And 4 more authors.
Experimental Physiology | Year: 2010

Since the first recording of sympathetic nerve activity (SNA) early last century, numerous methods for presentation of the resulting data have developed. In this paper, we discuss the common ways of describing SNA and their application to chronic recordings. Suggestions on assessing the quality of SNA are made, including the use of arterial pressure wave-triggered averages and nasopharyngeal stimuli. Calculation of the zero level of the SNA signal from recordings during ganglionic blockade, the average level between bursts and the minimum of arterial pressure wave-triggered averages are compared and shown to be equivalent. The use of normalization between zero and maximal SNA levels to allow comparison between groups is discussed. We recommend that measured microvolt levels of integrated SNA be presented (with the zero/noise level subtracted), along with burst amplitude and frequency information whenever possible. We propose that standardization of the quantifying/reporting of SNA will allow better comparison between disease models and between research groups and ultimately allow data to be more reflective of the human situation. © 2010 The Physiological Society.

Wang B.,University of Auckland | Hu A.P.,University of Auckland | Budgett D.,University of Auckland | Budgett D.,Telemetry Research Ltd
IEEE Transactions on Biomedical Circuits and Systems | Year: 2012

This paper proposes a new control method for regulating power flow via transcutaneous energy transfer (TET) for implantable heart pumps. Previous work on power flow controller requires a fast feedback loop that needs additional switching devices and resonant capacitors to be added to the primary converter. The proposed power flow controller eliminates these additional components, and it relies solely on a slow feedback loop to directly drive the primary converter to meet the heart pump power demand and ensure zero voltage switching. A controlled change in switching frequency varies the resonant tank shorting period of a current-fed push-pull resonant converter, thus changing the magnitude of the primary resonant voltage, as well as the tuning between primary and secondary resonant tanks. The proposed controller has been implemented successfully using an analogue circuit and has reached an end-to-end power efficiency of 79.6% at 10 W with a switching frequency regulation range of 149.3 kHz to 182.2 kHz. © 2011 IEEE.

Booth L.C.,University of Auckland | Bennet L.,University of Auckland | Guild S.,University of Auckland | Guild S.,Telemetry Research Ltd | And 5 more authors.
Experimental Physiology | Year: 2011

Sympathetic nerve activity (SNA) has two main properties, the presence of co-ordinated bursts of activity, indicative of many nerve fibres firing at a similar time, and entrainment of the bursts to the cardiac cycle, due to inhibitory input from baroreceptors to a network of cell groups within the CNS. Although this patterning is used as a 'gold standard' for the identification of successful nerve recordings, the maturation of these basic features of SNA from fetal life to adulthood has not been investigated. Using a telemetry-based nerve amplifier, renal SNA (RSNA) was recorded in preterm (99 ± 1 days gestation; term 147 days) and near-term fetal sheep (119 ± 0 days gestation), without anaesthesia or paralysis, and contrasted with RSNA recorded in adult sheep. All three age groups showed a classic bursting pattern of RSNA and co-ordination of bursts with the cardiac cycle. However, the delay between diastole and the next peak in RSNA was longest in preterm fetuses (319 ± 1 ms), compared with near-term fetuses (250 ± 13 ms), and shortest in the adult sheep (174 ± 38 ms). This was independent of the maturational decrease in heart rate. The near-term fetuses showed a marked but sleep-state-dependent increase in resting RSNA compared with preterm fetuses. Although entrainment with the pressure pulse suggests that the intricate circuitry within the CNS is developed in the preterm fetus, the decrease in the length of the delay suggests continuing maturation of this key feature of RSNA in the last third of gestation and after birth. © 2010 The Authors. Journal compilation © 2011 The Physiological Society.

Wang B.,University of Auckland | Hu A.P.,University of Auckland | Budget D.M.,University of Auckland | Budget D.M.,Telemetry Research Ltd
Proceedings of the 2010 5th IEEE Conference on Industrial Electronics and Applications, ICIEA 2010 | Year: 2010

A transcutaneous energy transfer system has been developed to provide the power required to drive an implanted heart pump. This will eliminate the risk of infection associated with the existing power transfer method - passing a wire through the skin. For implanted devices, particularly heart pumps which need large amount of power to operate, reducing heat generation is always of interest, and this paper proposes the use of a synchronous rectifier topology. A push-pull current doubler topology has been used due to its simple topology with only two low side MOSFETs to drive. The control circuitry has three stages, including voltage detection, controller and gate driver, to ensure the synchronous MOSFETs bypass the parallel Schottky diodes, and can operate at a high frequency (180kHz) with zero voltage switching. Practical efficiency measurements have shown that the main circuit of the current doubler synchronous rectifier has lower power losses than its Schottky only counterpart, however there is a need to further reduce the power loss of the control circuitry to realise the full potential of the proposed synchronous rectifier. © 2010 IEEE.

Wang B.,University of Auckland | Hu A.P.,University of Auckland | Budgett D.,Telemetry Research Ltd
Proceedings of the IEEE International Conference on Industrial Technology | Year: 2013

In order to reduce the power loss and associated temperature rise in the implanted side of the transcutaneous energy transfer system, the passive Schottky current doubler rectifier is replaced with an autonomous synchronous rectifier. Two options of driving the synchronous rectifier are proposed, passive autonomous operation and active gate drive using a buffer circuit. The synchronous rectifiers are found to have about 1.3% higher end-to-end efficiency compared to the Schottky only current doubler for the rated heart pump operational power of 10W. © 2013 IEEE.

Booth L.C.,University of Auckland | Gunn A.J.,University of Auckland | Malpas S.C.,University of Auckland | Malpas S.C.,Telemetry Research Ltd | And 5 more authors.
Experimental Physiology | Year: 2011

Late preterm infants, born between 34 and 36 weeks gestation, have significantly higher morbidity than neonates born at full term, which may be partly related to reduced sensitivity of the arterial baroreflex. The present study assessed baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in near-term fetal sheep at 123 ± 1 days gestation. At this age, although fetuses are not fully mature in some respects (term is 147 days), sleep-state cycling is established [between high-voltage, low-frequency (HV) and low-voltage, high-frequency (LV) sleep], and neural myelination is similar to the term human infant. Fetal sheep were instrumented to record blood pressure (BP), HR (n= 15) and RSNA (n= 5). Blood pressure was manipulated using vasoactive drugs, phenylephrine and sodium nitroprusside. In both HV and LV sleep, phenylephrine was associated with increased arterial BP and decreased HR. In HV sleep, phenylephrine was associated with a fall in RSNA, from 124 ± 14 to 58 ± 11% (P< 0.05), but no significant change in RSNA in LV sleep. In contrast, the fall in BP after sodium nitroprusside was associated with a significant increase in HR during LV but not HV sleep, and there was no significant effect of hypotension on RSNA. These data demonstrate that in near-term fetal sheep baroreflex activity is only partly active and is highly modulated by sleep state. Critically, there was no RSNA response to marked hypotension; this finding has implications for the ability of the late preterm fetus to adapt to low BP. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.

Wu Y.,University of Auckland | Hu A.P.,University of Auckland | Budgett D.,University of Auckland | Malpas S.C.,Telemetry Research Ltd. | Dissanayake T.,University of Auckland
IEEE Transactions on Biomedical Circuits and Systems | Year: 2011

Transcutaneous energy transfer (TET) enables the transfer of power across the skin without direct electrical connection. It is a mechanism for powering implantable devices for the lifetime of a patient. For maximum power transfer, it is essential that TET systems be resonant on both the primary and secondary sides, which requires considerable design effort. Consequently, a strong need exists for an efficient method to aid the design process. This paper presents an analytical technique appropriate to analyze complex TET systems. The system's steady-state solution in closed form with sufficient accuracy is obtained by employing the proposed equivalent small parameter method. It is shown that power-transfer capability can be correctly predicted without tedious iterative simulations or practical measurements. Furthermore, for TET systems utilizing a current-fed push-pull soft switching resonant converter, it is found that the maximum energy transfer does not occur when the primary and secondary resonant tanks are tuned to the nominal resonant frequency. An optimal turning point exists, corresponding to the system's maximum power-transfer capability when optimal tuning capacitors are applied. © 2010 IEEE.

Chen F.-Y.B.,University of Auckland | Wang B.,University of Auckland | Hu A.P.,University of Auckland | Budgett D.,Telemetry Research Ltd
Proceedings of the IEEE International Conference on Industrial Technology | Year: 2013

This paper proposes a novel zero voltage switching control method for a push-pull primary resonant converter by regulating its primary resonant shorting period. Also, the same inductive power transfer channel is used to establish a low bandwidth communication channel between the primary and secondary circuits based on frequency disturbance and temporary shorting of the power pickup. Practical results show that the system is able to track zero-voltage switching frequency automatically under variations of load, magnetic coupling, and other circuit parameters; and at the same time it can transmit and detect simple low bandwidth ON or OFF signals between the primary and secondary circuits. © 2013 IEEE.

Pinkham M.I.,University of Auckland | Guild S.-J.,University of Auckland | Guild S.-J.,Telemetry Research Ltd | Malpas S.C.,University of Auckland | And 2 more authors.
Experimental Physiology | Year: 2012

The physiological mechanisms contributing to sex differences following myocardial infarction (MI) are poorly understood. Given the strong relationship between sympathetic nerve activity (SNA) and outcome, we hypothesized there may be a sex difference in SNA responses to MI. In anaesthetized, open-chest male, female and ovariectomized (OVX) female Wistar rats, mean arterial pressure, heart rate and renal SNA were recorded in response to ligation of the left coronary artery. In males, renal SNA increased by 30 ± 6% in the first minute of coronary occlusion (P < 0.05) and remained elevated at 18 ± 7% above baseline (P < 0.05) at 2 h following MI. In response to MI, ovary-intact females displayed no change in renal SNA, whereas OVX females displayed a significant increase, similar to that seen in the males (increases of 43 ± 11% at 1 min and 21 ± 7% at 2 h post-MI, P < 0.05 versus intact females). Arterial baroreflex control of renal SNA had a smaller range in females (ovary intact and OVX) than males; no changes in arterial baroreflex responses were observed 1 h post-MI in males or females. Denervating the arterial baroreceptors abolished the renal SNA response to MI in the males, whereas in ovary-intact females and OVX females the response was unaltered. These findings suggest that ovarian hormones are able to blunt the initial sympathetic activation post-MI in females and that the importance of the arterial baroreflex in mediating initial sympathetic activation post-MI is different between the sexes. © 2012 The Physiological Society.

TELEMETRY RESEARCH Ltd | Date: 2011-09-09

In one embodiment of the invention a catheter (203) comprises a body having at least one inlet aperture (21, 24), at least one outlet aperture (22, 25), and at least one passage (20, 23) between the at least one inlet aperture (21, 24) and the at least one outlet aperture (22, 25). The catheter (203) is provided with pumping means (32) for selectively pumping fluid from one of said apertures (21, 22, 24, 25) to another of said apertures (21, 22, 24, 25). Methods of operating such a catheter are also disclosed.

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