Principles of Biomedical Sciences: Activity 1.2.2 Time of Death

Flashcards covering definitions of time of death, postmortem indicator timelines, temperature conversions, formulas, and forensic case scenario calculations from Activity 1.2.2.

How is the physiological time of death defined?

The time when the decedent's vital functions actually ceased.

How is the estimated time of death defined?

The time the medical examiner estimates that the death occurred.

How is the legal time of death defined?

The time of death recorded on the death certificate; based on when the body was found or physically pronounced dead.

Why is determining the exact physiological time of death often difficult for forensic investigators?

There is no single factor that will accurately indicate the time of physiological death.

Which three factors are listed in Part 1 as postmortem changes that occur after death?

Algor mortis, Rigor mortis, and Livor mortis.

What is the typical timeframe and description of Algor Mortis?

Occurs between $0\text{--}24\text{ hours}$ after death; body temperature typically reaches the temperature of the surrounding environment within $24\text{ hours}$ of death.

What is the typical timeframe and physical characteristic of clouding of the corneas?

Occurs within $3\text{--}4\text{ hours}$ after death; within the first several hours, the corneas (which are usually clear) become milky or cloudy.

What is the typical timeframe and characteristic mechanism of Livor Mortis (lividity)?

Occurs between $0\text{--}24\text{ hours}$ after death; when the heart stops beating, the blood is at the mercy of gravity.

What is the typical timeframe and physical change associated with Rigor Mortis?

Occurs between $2\text{--}4\text{ hours}$ after death; after the body stops functioning, the muscles contract and stiffen.

What is the typical timeframe and physical description of decomposition?

Occurs between $36\text{--}48\text{ hours}$ after death; the body turns greenish in color and may swell or bloat as bacteria break down tissue and release gas.

What is the typical timeframe for insect activity on a body, and what information does it provide?

Occurs between $1\text{--}145\text{ hours}$ after death; the presence of eggs, larva, or full-grown bugs provides a timestamp for how long the body has been decaying.

What formula is used to convert Celsius temperature to Fahrenheit?

$$\text{Fahrenheit}(^\circ\text{F}) = (\text{Celsius}(^\circ\text{C}) \times 1.8) + 32$$

What are the calculated Fahrenheit temperatures for $20^\circ\text{C}$, $37^\circ\text{C}$, and $10^\circ\text{C}$?

$20^\circ\text{C} = 68^\circ\text{F}$, $37^\circ\text{C} = 98.6^\circ\text{F}$, and $10^\circ\text{C} = 50^\circ\text{F}$.

What baseline normal body temperature and average cooling rate are assumed in Algor Mortis calculations?

Normal living body temperature is assumed to be $98.6^\circ\text{F}$ ($37^\circ\text{C}$), and the average rate of cooling is $1.5^\circ\text{F}\text{ per hour}$.

What is the formula used to calculate Hours Since Death based on body cooling?

$$\text{Hours Since Death} = \frac{\text{Normal Body Temp } (98.6^\circ\text{F}) - \text{Measured Body Temp}}{1.5^\circ\text{F}/\text{hour}}$$

What is the formula used to determine the Estimated Time of Death (TOD)?

$$\text{Estimated Time of Death (TOD)} = \text{Time Body Found} - \text{Hours Since Death}$$

In Scenario 1, a body is discovered at 10:00 a.m. with an internal temperature of $89^\circ\text{F}$. What are the total degrees lost, hours passed, and estimated physiological time of death?

Total degrees lost: $9.6^\circ\text{F}$; hours passed since death: $6.4\text{ hours}$; estimated physiological time of death: 3:36 a.m.

In Scenario 2, investigators arrive at 4:00 p.m. and find a body temperature of $91.1^\circ\text{F}$. What are the hours passed since death and the calculated estimated time of death?

Hours passed since death: $5\text{ hours}$; calculated estimated time of death: 11:00 a.m.

In Scenario 2, does early rigor mortis in the face/neck and light un-fixed livor mortis support a calculated time of death of 11:00 a.m. (5 hours prior)?

Yes. Early rigor mortis in the face/neck and light, unfixed livor mortis are consistent with relatively early stages after death.

In Scenario 3, a victim is found at 8:00 a.m. with an internal temperature of $31^\circ\text{C}$. What are the Fahrenheit conversion, degrees lost, hours since death, and estimated time of death?

Temperature in Fahrenheit: $87.8^\circ\text{F}$; total degrees lost: $10.8^\circ\text{F}$; hours since death: $7.2\text{ hours}$; estimated time of death: 12:48 a.m.

In Scenario 4, Freddy's body is found at 10:00 a.m. with an internal body temperature of $86.6^\circ\text{F}$. What are the hours postmortem and estimated time of death?

Hours postmortem: $8\text{ hours}$; estimated time of death: 2:00 a.m.

In Scenario 4, why should investigators question Suspect A further rather than Suspect B regarding Freddy's death?

The estimated time of death is around 2:00 a.m., and Suspect A claims he was with Anna until exactly 2:00 a.m., making his alibi warrant further investigation.