Due by Saturday, 11:59 p.m. (MT) end of Week 1 (120 pts)
Learning Objectives Covered
1. Explain Negative pressure ventilation
2. Describe how the ventilator functions and how input power is converted to ventilator breaths, how breaths are controlled by the ventilator and the variables that describe the modes of ventilation
3. List and describe the three phase variables for a mechanical breath to be delivered: Trigger, Limit, and Cycle
Background
 
Negative pressure ventilators were inspired in the early 1900’s, before the polio epidemic, to provide artificial respiration. The use of negative pressure ventilators today is rare but understanding their use helps provide a greater understanding of ventilators. Negative pressure ventilators were intended to mimic natural spontaneous breathing by creating pressure gradients around the patient’s chest. They provided noninvasive ventilation, which was accomplished by using either a shell that surrounded the chest or a cylinder that enclosed the entire body. The principle of these devices is that a vacuum pump created subatmospheric pressure (negative pressure) intermittently in a chamber surrounding the thorax (chest wall) which resulted in the expansion,of the patient’s chest initiating inspiration. When the vacuum was terminated, the negative pressure outside the chest wall returned to zero and the elastic recoil of the chest and lungs permitted passive exhalation allowing air to flow out of the lungs into the atmosphere. When negative pressure is being applied to the thorax air flows into the lungs from the atmosphere.
There are two primary types of negative pressure ventilators: Iron lung and chest cuirass. An iron lung is a device where the entire body, except for the head, is placed in a chamber with an airtight seal around the neck. A chest cuirass is a jacket with seals around the neck, arms, and thighs. The chest cuirass was suitable for home use and provided much more versatility than the iron lung.
Modern mechanical ventilators use positive pressure to provide ventilatory support. Positive-pressure ventilation is an invasive technique that uses an endotracheal or tracheostomy tube to push gas directly into a patient’s lungs until the machine terminates the breath. The pushing of gas into the patient’s lungs creates positive pressure as opposed to negative pressure, which is created by the downward pull of the diaphragm and the outward expansion of the chest wall creating pressure gradients and therefore causing air to flow into the lungs.
Input power is simply the power source that enables a device to function. The power source provides a ventilator with the energy to perform the work required to ventilate a patient. A power source may be an electric or gas source. Ventilators that are electrically powered are most commonly used in homes. Ventilators that use a 50psi gas source are referred to as pneumatically-powered and are most commonly used for transporting ventilator dependent patients throughout the hospital or during an MRI. Patients that use both electrical and pneumatic power are referred to as combined powered ventilators and are most commonly used in the Intensive Care Units (ICU).
It is important to note that when reference is made to a ventilator breath it implies that the  inspiratory phase of a breath is delivered and exhalation is always passive. In order to understand mechanical ventilation one must understand the phases of inspiration during ventilation. There are three phases of inspiration. The beginning (how and when inspiration starts), the middle (how much air enters the lungs and how much the lungs expand), and the end (how and when inspiration ends). Mechanical ventilation uses ventilators to deliver gas to the lungs using positive pressure at a certain rate (respiratory rate). The amount of gas delivered can be limited by time, pressure, volume, or flow. The duration of inspiration can be cycled(terminated) by time or volume. There are three phase variables that define the parameters of a ventilator breath. The three parameters are set by the clinician on the machine and include: how the breath begins (trigger), how the breath is delivered (limit), and how the breath ends (cycle). Another equally important parameter that is also set by the clinician determines how often a breath is delivered (respiratory rate).
How a mechanical breath begins is defined by the trigger variable. The breath trigger variable is known as the sensitivity control. The limit variable places a maximum value or limit on a control variable during delivery of a breath. During mechanical ventilation of an adult the limit or control variable can be pressure limited or volume limited. A limit variable is a parameter that rises to a certain value but does not exceed it. For example, a patient with ARDS has extremely non-compliant lungs (stiff lungs). When ventilating these patients, care must be taken during mechanical ventilation to not over distend the lungs, which can result in a pneumothorax and further damage to the lungs. These patients are placed on pressure control also known as pressure limited ventilation and a pressure level is set. Once the breath is triggered (begins) then the machine will deliver pressure and the pressure will rise until it reaches the preset level. Once the preset pressure level is reached then it is maintained at that level until inspiration ends. The cycle variable is the parameter that ends the inspiratory phase and allows passive exhalation to begin. During pressure control ventilation the cycle variable is time. An inspiratory time (I time) is set and once the set time elapses then inspiration ends. During volume control ventilation the amount of air to be delivered during inspiration (tidal volume) is set and when the set volume is reached inspiration ends. Therefore, it is important to remember that pressure control/pressure limited ventilation is time cycled and volume control/volume limited ventilation is volume cycled.
There are three primary types of breaths delivered by a ventilator: mandatory, assisted, and spontaneous. A mandatory breath indicates that the ventilator does all the work of breathing and the patient does none of the work required to breathe. This type of breath allows the patient to fully rest their inspiratory muscles. During a mandatory breath all three phases of inspiration are controlled. The ventilator starts the breath, controls inspiratory gas delivery and determines when inspiration ends. An assisted breath is a breath in which the patient does some of the work, however, the patient is only allowed to start or initiate a breath. Once inspiration begins the ventilator then takes over and controls the inspiratory phase and determines when inspiration ends. Therefore, during an assisted breath only 2 of the 3 phases of inspiration is controlled. A spontaneous breath is a breath in which the patient controls all phases of inspiration which means that the patient does all the work required to breathe. The ventilator monitors the patient parameters, notifies clinicians of issues through set alarms and serves as a backup if the need arises.
Prompt
For this assignment, you will provide detailed responses to the following questions
1. Discuss the effects of positive pressure ventilation on oxygenation and ventilation
2. Define the following terms and explain their significance
· Peak inspiratory Pressure (PIP)
· Plateau pressure (Pplat)
· Airway resistance (Raw)
· Dynamic Compliance (Cdyn)
· Static Compliance (Cstat)
3. Define each of the ventilator modes listed below:(use your own words)
· Continuous Mandatory Ventilation
· Synchronized Intermittent Mandatory Ventilation
· Pressure Support Ventilation
· Continuous Positive Airway Pressure
Submit your answers in at least 500 words on a Word document. You must cite at least three references in APA format to defend and support your position.

Chapter 8 Discussion – Personal Assessments of HIV Risk
Chapter 8 was a little overwhelming. There were so many theoretical descriptions of how people make decisions about their choice of sex partners, and other risky behaviors. Does anyone actually think like this? The truth is, that most of us make potentially life altering decisions in the blink of an eye. Yet behind those split-second decisions, there is an evolutionary history, dating back to early man. Intuition, as we might call it, is probably an unconscious series of decisions made based on associations with people and lifetime experiences.  All of these flashes of memory are confounded in the present with fear, lust, emotion and other biases, well before logical thinking comes into the picture.
The best way to understand these concepts is probably not to read about them in a textbook, but to discuss them, bringing to mind our own experiences, and those of people whom we have known. The task for this discussion will be to give an example of how someone you have known or read about has used one of these decision-making models to make a life-altering decision in their own life, and how it has affected them. Remember, we should be focusing our discussion on the situation, not the person involved, so don’t identify any person by name.
If you can’t think of a real-life situation to use as an example, use a character from a well known book or movie, or explain a theoretical situation that might happen in real life. Or write something more general about one of these topics.
 
Examples:
a. Give an example of how optimistic bias has influenced the attitude of a young person about their risk of becoming infected with HIV.
b. Explain how the representative heuristic has led to an irrational fear in yourself, or someone you have known, that HIV can be transmitted by casual contact.
As usual, upload your post of 150-200 words.
Chapter 9 Discussion – Principles of Health Behavior Change
Read about the 7 principles of health behavior change in Chapter 9 p.160-166. These are the factors that need to be considered when developing programs to educate the public about behavioral change in promoting safe sex.
1. The Cognitive Principle
2. The Emotional Principle
3. The Behavioral Principle
4. The Interpersonal Principle
5. The Social Ecological Principle
6. The Structural Principle
7. The Scientific Principle
For the discussion this week, we will be practicing working with the principles above. Each of you should choose one of these principles. Explain the principle and how you would incorporate it when developing an AIDS prevention program. You can make up a scenario for a hypothetical target demographic, use an example or keep it general. You don’t need to develop an extensive educational program. You only need to develop the one aspect of a program that employs the principle that you are discussing.