Tag: current stimulator

Holiday Happiness: Gratitude or Gifts?

Studies investigated the anxiety of gift-giving, the effects of social support in stressful situations, and what impact meditation has on heart rate, ECG, and blood pressure.

December has arrived, and for many the holidays bring a rush to check items off of a long shopping list for parents, siblings, friends, in-laws, and many more. Often we struggle to find that “perfect” gift, but are the physical goods we exchange the true source of the warmth and happiness that characterizes the season?

An article by Nomura investigated anxiety induced by gift-giving. To test this, EDA data was recorded with a BIOPAC data acquisition system and STP100 while participants responded to stimuli. The participants visualized a specific relative while being presented with potential gift options, and were asked how likely they were to purchase the potential gift for that relative. The data found that people who self-reported thinking of in-laws were the most stressed, while those who reported thinking of children or same-gender friends were least stressed.

A psychosomatic study by Inagaki and Eisenberger found that mental and physical well-being benefit from forms of social support. They tested this by administering mild shocks with the BIOPAC STMISOLA to male patients who held the hand of a female partner lying in an fMRI. The results suggest that this support (hand-holding) provided possible stress-reduction for both the male and female participants.

Another article on nonverbal communication and well being by Shaltout, et al. tested the effects of meditation and the subsequent ECG, blood pressure, and heart rate effects. The BIOPAC ambulatory BioHarness and NIBP Blood Pressure System gathered data while participants underwent several mediation episodes, during which they were instructed to focus on loving kindness towards a subject. The results found that participants had decreased heart rate.

Research suggests direct, loving interactions with those who are close to us have many stress-reducing benefits. So when you are shopping for gifts, remember that spending time is more important than spending money. To read more studies about love and stress reduction, visit the BIOPAC publication page.

BIOPAC offers a variety of equipment that can be used in studies similar to the ones presented. To find more information on solutions for recording and analyzing signals such as EEG, EMG, respiration, and EDA using the MP160/MP150, MP36, and other platforms, you can visit the individual application pages on the BIOPAC website. 

BIOPAC Systems, Inc. provides life science researchers and educators with data acquisition and analysis systems that inspire people and enable greater discovery about life. Visit us at www.biopac.com.

Electrical Stimulators for Physiological Research

Highly-controlled electrical stimulation capability can provide a unique tool for the life science researcher to discern sensory function and associated physiological responses in living subjects. There are two types of electrical stimulators, voltage and current.

By Alan Macy, BIOPAC Systems, Inc.

Any physiological measurement is concerned with the subject of stimulus and response, because all physiological processes are subject to change with applied stimuli. The processes of life encapsulate the idea that environmental change precipitates sensory activity that results in stimulation. Because sensory activity is mediated by the flow of ions in the nervous system, highly controlled electrical stimulation capability can provide a unique tool for the life science researcher to discern sensory function and associated physiological responses in living subjects.

Computer-based systems can be used to define very exacting electrical stimuli and those signals can be directed to a subject via electrodes. The level of stimuli can be extremely wide and the shape of the stimuli can be finely controlled. Signals can be introduced directly into nerves or muscle fibers to evoke a specific response.

There are two types of electrical stimulators, voltage and current. A voltage stimulator behaves like a voltage source, in that it outputs a variable voltage with low output impedance. A current stimulator behaves like a current source, in that it outputs a variable current with high output impedance.

The primary physical expression that characterizes the behavior of electrical stimulators is:

Vs = Is * Zs

where:

Vs – stimulation voltage from stimulator
Is – stimulation current from stimulator
Zs – impedance of stimulation loop

Zs is the collective impedance of the complete stimulation loop. From a simplified view, Zs consists of the series combination of two electrode / skin junction impedances and the stimulated tissue volume. Zs has resistive and capacitive components, so the capacitive components charge in accordance to the expression:

Ics = Cs * (dVcs/dt)

where:

Ics – stimulation current through Cs
Cs – capacitive component associated with Zs
dVcs/dT – change in stimulus voltage, across Cs, as a function of time

Accordingly, electrical stimulation is associated with the charging of the stimulation loop capacitance. If fast electrical stimulation is required, then the stimulator should have high current level drive capability. For a given Cs, the speed of charging (dVcs/dt) will be higher (faster) as Ics is increased.

There are two major sub-impedances in the stimulation loop that define the portion of the stimulator output voltage (Vs) that is directly across the tissue volume (Vt):

Ze – electrode to site impedance (total of both sites)

Zt – stimulated tissue volume impedance

Vs = Is * Zs

Vs = Is * (Ze + Zt)

Vt = Vs * (Zt / (Ze + Zt))

Because of this relationship, the value of Vt might not be reliably specified, given a certain Vs.For any given tissue volume, electrical stimulation can be specified in terms of voltage across the tissue volume (Vt) or current through the tissue volume (It). In practice, because two terminal stimulation is simple to apply, current stimulation is often used because the current through the tissue volume (It) is the same as the sourced stimulation current (Is). However, if the stimulation current (It) is specified then Vt may be indeterminate. Sometimes, both (It) and (Vt) are required to be known, such as with bioimpedance measurements. In this case, voltage monitoring electrodes can be placed on the tissue volume so both (It) and (Vt) can be identified.

Compliance, an essential characteristic of electrical stimulators, is addressed in Electrical Stimulators for Physiological Research: Compliance.

BIOPAC Systems, Inc. provides life science researchers and educators with data acquisition and analysis systems that inspire people and enable greater discovery about life. BIOPAC lets you measure physiology anywhere, with innovative, compatible wireless, wearable solutions that can be used by anyone for meaningful discovery. We make high-quality scientific tools for physiology measurement and interpretation with superior compatibility and world-class customer service and support. Visit us at www.biopac.com.

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