the logic model (also known as a logical framework, theory of change, or program matrix) is a tool used by funders, managers, and evaluators of a program to evaluate its effectiveness. It is a graphical depiction of logical relationships between the resources, activities, outputs, and outcomes of a program (3, 7, 11, 12). Although there are many ways in which logic models can be presented, the underlying purpose of constructing a logic model is to assess the “if-then” (causal) relationship between the elements of a program. If resources are available for a program, then the activities can be implemented; if the activities are implemented successfully, then certain outputs and outcomes can be expected. A logic model thus has four major components: inputs, activities, outputs, and outcomes (3, 8, 9, 11, 12) (Table 1).
Physiology deals with normal functioning of the human body wherein various regulatory mechanisms work together to establish homeostatic environment. The understanding of homeostasis has evolved since its original formulation; however, the core concept captured by Cannon's phrase “Wisdom of the Body” remains its defining property (1). Wisdom of the body describes how an array of physiological and behavioral responses are elicited in a seemingly coordinated way to stabilize or defend critical physiological parameters. Blood pressure and blood sugar are the vital physiological variables, as defined by Walter Cannon in 1929, wherein homeostasis is the principle underlying physiological regulation for ongoing maintenance and defense. A fundamental tenet of homeostatic regulation is that variables work together in a coordinated fashion to wisely defend bodily parameters critical to well being (2). They are programmed in such a way that, if one input falters, there are multiple alternative mechanisms to regulate. The body is accustomed to such mechanisms, which in technological terms can be considered as a program. The array of inputs through their respective mechanisms work in unison to achieve a defined product (i.e., output and outcome).
This principle of regulated outcome, as explained through the logic model, can help in understanding physiological principles to maintain homeostasis. We explored this model by fitting in the inputs, processes, outputs, and outcomes for teaching arterial blood pressure (ABP) regulation to undergraduate students of first phase in medicine.
This idea was developed to design a logic model of ABP regulation (Table 2) for undergraduate students of first phase in subject of Physiology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences (Deemed University). The description in brief is as follows (6).
Blood pressure is the pressure exerted by blood on walls of the arteries. Various inputs that are instrumental in physiological regulation of blood pressure can be grouped into the following:
A. General factors: general factors are physiological factors that determine the range of blood pressure, viz., age, sex, hereditary, meals, sleep, emotions, gravity, and diurnal variations.
B. Circulatory factors: the major circulatory factor that can cause alteration is mainly cardiac output, which depends on stroke volume and peripheral resistance. Stroke volume is the amount of blood ejected by each ventricle per beat. It is dependent mainly on myocardial contractility and end-diastolic volume. Peripheral resistance is the resistance offered by the arterial system to the outflow of blood. Factors that determine peripheral resistance are 1) arteriolar radius, which depends on intrinsic, i.e., myogenic and metabolic factors and extrinsic, i.e., hormonal, paracrine, and neurogenic factors; 2) length of the vessel; 3) and viscosity of blood. This flow-pressure-resistance relationship can be explained by Poiseuille-Hagen law (4, 5, 10, 13, 14). Other important factors are elasticity of vessel wall and velocity of blood flow.
All of these inputs lead to four major physiological processes taking place in the body to keep blood pressure variations within normal limits. The activities occur either simultaneously or one after the other. The activities can be grouped into the following: 1) nervous regulation (sympathetic and parasympathetic systems), 2) intrinsic physical regulatory mechanisms, 3) autoregulatory mechanisms, and 4) hormonal mechanisms.
The various processes as mentioned above have different areas of operation. They can be grouped into short, intermediate, and long-term mechanisms. The output through short-term mechanism will be correction for momentary changes in blood pressure; for intermediate, it will be correction for variations for a brief period; and for the long term, it will be correction leading to complete equilibrium for years. Resultantly the sources of these outputs will be as follows (6):
1. Short-term mechanism
A. Baroreceptor reflex (60–100 mmHg): baroreceptors are located mainly in carotid sinus and aortic arch. The cells are sensitive to pressure, hence the name “baroreceptors”. When pressure rises, they send impulses to vasomotor center (VMC) and increase the parasympathetic tone to bring back the ABP to normal limits.
B. Chemoreceptor reflex (40–60 mmHg): tissue ischemia stimulates peripheral chemoreceptors (carotid and aortic bodies), resulting in rise in blood pressure, heart rate, and rate and depth of respiration by stimulation of VMC and respiratory center.
C. CNS ischemic response (15–50 mmHg): a fall in blood pressure below 50 mmHg can directly stimulate VMC. Resultant stimulation of sympathetic nervous system increases heart rate, cardiac output, and blood pressure. This phenomenon is also observed in increased intracranial tension that occludes blood supply to brain due to compression of arteries. The CNS ischemic response thus initiated is also referred to as “Cushing's Reflex”.
2. Intermediate-term mechanism
A. Capillary fluid shift (+30 to 15%): This is a simple anatomic shift of capillary fluid to the extracellular space whenever the blood pressure rises. The shift in fluid leads to a decrease in blood volume and resultant fall in pressure.
B.Stress relaxation and reverse stress relaxation: the phenomenon of accommodating extra blood by relaxation of arterial wall is known as stress relaxation, and the process of arterial contraction due to fall in blood volume is known as reverse stress relaxation.
3. Long-term mechanism: the long-term mechanisms are the most effective ones in maintaining the blood pressure within narrow range throughout life. This is brought about by direct as well as indirect mechanisms. The direct mechanisms of long-term regulation are achieved mainly through pressure diuresis and pressure natriuresis, and indirect mechanisms are through hormonal mechanisms. The hormonal mechanisms bring about mechanical changes in the wall of the renal arteries like vasoconstriction and also alter the absorptive properties of renal tubules. The two main hormonal mechanisms are as follows:
A. Renin-angiotensin-aldosterone mechanism.
B. Antidiuretic hormone.
The long-term impact depends upon the type of mechanisms causing the output. Short-term mechanisms control the blood pressure for seconds to minutes. Intermediate-term mechanisms control the pressure for minutes to hours and long-term mechanism for years together.
Implementation Strategy and Finding
This educational project was piloted for medical students in the first phase through convenient sampling. The undergraduate intake capacity of the university is 200 students/year, who, for teaching learning purposes, are divided into batches A and B, with 100 students in each batch. For the present study, batch A students were considered as an experimental group (n = 95). Five students were absent on the day of project, and hence, they were were not included. Batch B students were considered as controls (n = 93). Two students were on medical leave and five were absent (total of 7), and hence, they were not included in the study. The objectives were as follows:
1.Sensitize the experimental group about the importance and implication of logic model.
2.Aid in the understanding of blood pressure regulation through logic model, thereby stressing the importance and correlation of input, process, output. and outcomes for maintaining blood pressure within physiological limits.
3.Compare the level of understanding of blood pressure regulation between experimental group (n = 95) and controls (n = 93).
4.Record the perception of experimental groups regarding learning through logic model.
5.Analyze the limitations of this approach.
The experimental group (n = 95) was first briefed about logic model (lecture based) so that they understood the concept in a better way. They were taught about ABP regulation by logic model, and controls were taught the same in conventional way (n = 93). Two objectives of the class were identified. 1) Learners should be able to enumerate various regulatory factors for ABP regulation; 2) they should be able to explain various mechanisms that are involved in maintaining short-, intermediate-, and long-term ABP within physiological limits.
Student perceptions of the utility of this method were collected in a feedback tool with three simple close-ended items and one open-ended item. Out of the 95 students who attended, 90.5% agreed or strongly agreed that the concept of logic model is interesting. It was agreed by 84.1% of students that the new approach could be helpful in retaining and reproducing the concept of ABP regulation. Experimental group further affirmed (91.57%) that they would like to explore the logic model further. In response to the question, “Where else can the principle of logic model be applied in physiology?”, 45 and 12% students mentioned regulation of respiration and hormonal regulation, respectively, and 43% did not comment (Table 3). Learning on preidentified objectives (as mentioned above) was assessed through semistructured oral examination by four examiners on a preagreed rating scale. It had questions and model answers pertaining to factors regulating ABP and various mechanisms of regulation. The average score was 14 and 13.5 out of 20 for the experimental group and controls respectively, which was not statistically significant.
We will extend this pilot study of the logic model to other systems in physiology and design a logic model curriculum for regulation of respiration, cardiac output, glomerular filtration, hormonal regulation and heat regulation. The new study will be expanded with a randomized controlled crossover design for testing the hypothesis.
Implications of Logic Model for Blood Pressure Regulation
The proposed model will help learners understand the regulation of ABP with reference to different physiological inputs that work together to keep it within normal limits. The logical sequence of outcomes in terms of short-, intermediate- (control mechanisms), and long-term regulation (regulatory mechanisms) can be comprehended and retained in a better way. Although the present short project did not give significant results, embedding the framework of the logic model into other parts of the physiology curriculum might aid in understanding the significance of association between inputs and outcomes. It can also emphasize the importance of different factors and their interplay in attaining homeostasis.
No conflicts of interest, financial or otherwise, are declared.
L.S.W. drafted manuscript; L.S.W. approved final version of manuscript; T.k.S. conception and design of research; T.k.S. edited and revised manuscript.
- Copyright © 2016 The American Physiological Society